Reinforcing nanofiber additives

ABSTRACT

Provided herein are high performance reinforcing nanostructure additives, high throughput processes for using such additives, and composites comprising such additives. Such nanostructure additives include nanofibers, including nanofiber fragments, of various matrix materials, including metal(s) (e.g., elemental metal(s), metal alloy(s), etc.), metal oxide(s), ceramic(s), metal carbide(s), carbon (e.g., carbon nanocomposites comprising carbon matrix with metal component embedded therein), and/or combinations thereof.

CROSS-REFERENCE

This application is a Continuation of U.S. application Ser. No.14/428,435 filed Mar. 16, 2015, which is a U.S. National Phase filing ofInternational Application No. PCT/US2013/059894 filed Sep. 16, 2013,which itself derives priority from U.S. Provisional Application Ser. No.61/701,889, filed Sep. 17, 2012, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

Manufacturers mix additive materials with matrix materials to optimizeand enhance properties, improve performance, and/or decrease costs ofbulk materials.

SUMMARY OF THE INVENTION

Provided herein are reinforcing nanostructure additives, compositescomprising reinforcing nanostructure additives, and processes forproducing reinforcing nanostructure additives. In specific embodiments,reinforcing nanostructures comprise nanofibers, and/or fragmentsthereof. In some embodiments, reinforcing nanostructures provided hereincomprise at least one metal component (e.g., metal, metal oxide, metalcarbide, ceramic, or combinations thereof). In specific embodiments, themetal component comprises at least one metal in an oxidation state ofzero or greater (e.g., 0-4). In certain embodiments, the reinforcingnanostructures comprise (a) metal nanofibers, and/or fragments thereof;(b) metal oxide nanofibers, and/or fragments thereof; (c) metal carbidenanofibers, and/or fragments thereof; or (d) ceramic nanofibers, and/orfragments thereof. In some embodiments, the metal component comprises atleast two metals (e.g., a metal-metal alloy). In certain embodiments,the at least one metal component comprises at least two metal components(e.g., a nanocomposite nano structure).

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates a schematic of an apparatus and process for preparingnanostructures described herein.

FIG. 2 illustrates a coaxial electrospinning apparatus useful forproducing nanostructures described herein.

FIG. 3 illustrates an exemplary mechanism for loading of metal precursoronto polymer (e.g., in an aqueous medium).

FIG. 4 illustrates an FTIR spectrum demonstrating the increased loadingof metal precursor onto polymer (PVA).

FIG. 5 illustrates various precursor nanofibers prepared according toprocesses described herein.

FIG. 6 illustrates exemplary metal nanostructures (nanofibernanostructures) provided herein.

FIG. 7 illustrates various precursor nanofibers and metal carbidenanofiber nanostructures described herein and prepared according toprocesses described herein.

FIG. 8 illustrates metal carbide nanofiber nanostructures preparedaccording to the process described herein, as well as X-Ray Diffractiondata therefor.

FIG. 9 illustrates an exemplary nanostructure nanocomposite.

FIG. 10 illustrates exemplary metal oxide nanostructures (nanofibernanostructures) provided herein.

FIG. 11 illustrates exemplary nanocomposite nanostructures (nanofibernanostructures) provided herein

FIG. 12 illustrates the electrical conductivity of certain metalnanostructures provided herein (and their relative values compared toknown bulk values for the same metals).

FIGS. 13A-13C illustrates the X-Ray Diffraction (XRD) data for exemplarymetal, metal oxide, and nanocomposite nanostructures provided herein.

DETAILED DESCRIPTION OF THE INVENTION

Provided herein are nanostructure materials, composites comprisingnanostructure materials, and processes for producing such nanostructurematerials. In some instances, such nanostructures and compositionscomprising a plurality of such nanostructures are used as or useful asadditives for bulk materials. In certain instances, these nanostructuresare nanofibers, or are fragments of or prepared from nanofibers, such asby fracturing nanofibers into fragments thereof. In some embodiments,addition of such additives to a bulk material serves to reinforce thebulk material. In further embodiments, reinforcement of the bulkmaterial with such additives improves the performance of a material,reduces the costs of a material, or provides other benefits thereto. Ingeneral, the processes described herein provide the ability to preparenanostructures with improved performance properties over othernanostructures, such as those prepared by sol gel electrospinning, lowloading solution electrospinning, nanowire growth, and the like.

In some embodiments, reinforcing nanostructures provided herein compriseat least one metal component (e.g., metal, metal oxide, metal carbide,ceramic, or combinations thereof). In specific embodiments, the metalcomponent comprises at least one metal in an oxidation state of zero orgreater (e.g., 0-4). In specific embodiments, the nanofibers are high inmetal content (e.g., on an elemental wt % basis).

Also, provided in certain embodiments herein is a process for producingreinforcing nanostructure additives, the process comprising (a) treating(e.g., thermally treating) an electrospun nanofiber comprising a metalreagent component (e.g., metal precursor) and a polymer; and (b)optionally fracturing the treated nanofiber (e.g., via sonication). Insome embodiments, the electrospun nanofiber comprising a metal reagentcomponent (e.g., metal precursor) and a polymer is prepared byelectrospinning a fluid stock, the fluid stock comprising (1) a metalreagent component; and (2) polymer. In specific embodiments, the metalreagent component comprises a metal precursor, a metal oxidenanoparticle, a metal nanoparticle, or a combination thereof. In morespecific embodiments, the metal reagent component is a metal precursor.

Nanostructure Composition/Additive

In some instances a nanostructure or plurality of nanostructuresprovided herein comprise, on average, at least 20% by weight of the atleast one metal component. In more specific embodiments, the metalcomponent constitutes, on average, at least 33% of the nanostructure(s).In still more specific embodiments, the metal component constitutes, onaverage, at least 50% of the nanostructure(s). In yet more specificembodiments, the metal and component constitutes, on average, at least70% of the nanostructure(s). In more specific embodiments, the metalcomponent constitutes, on average, at least 90% of the nanostructure(s).In various embodiments, the metal component constitutes, on average, atleast 10%, at least 25%, at least 40%, at least 60%, at least 75%, atleast 80%, at least 95%, at least 97%, at least 98%, or at least 99% ofthe nanostructure(s).

In some instances a nanostructure or plurality of nanostructuresprovided herein comprise, on average, at least 20 elemental wt. % metal.In more specific embodiments, metal constitutes, on average, at least 33elemental wt. % of the nanostructure(s). In still more specificembodiments, metal constitutes, on average, at least 50 elemental wt. %of the nanostructure(s). In yet more specific embodiments, metalconstitutes, on average, at least 70 elemental wt. % of thenanostructure(s). In more specific embodiments, metal constitutes, onaverage, at least 90 elemental wt. % of the nanostructure(s). In variousembodiments, metal constitutes, on average, at least 10 elemental wt. %,at least 25 elemental wt. %, at least 40 elemental wt. %, at least 60elemental wt. %, at least 75 elemental wt. %, at least 80 elemental wt.%, at least 95 elemental wt. %, at least 97 elemental wt. %, at least 98elemental wt. %, or at least 99 elemental wt. % of the nanostructure(s).

In some embodiments, provided herein are high quality nanostructureadditives and processes for preparing high quality nanostructureadditives that have good structural integrity, few voids (e.g., having aregion so narrow as to cause the nanostructure to be so narrow as to bebrittle or have low conductivity, or having regions missing so as tohave a discontinuous structure), few structural defects (e.g., amorphousregions an otherwise crystalline nanostructure, crystalline regions inan otherwise amorphous nanostructure, or the like), tunable length, andthe like. In some instances, voids or structural defects lead todecreased performance of the nanostructure additives. For example, insome instances, voids or structural defects cause the nanostructureadditives to have decreased strength, fracture toughness, conductivity,or the like. In one example, voids and defects in the nanofiber includebreaks in the nanofiber, regions of nanofiber wherein the diameter is sonarrow as to be easily broken (e.g., having a diameter of less than 10%or less than 5% of the average nanofiber diameter), regions of thenanofiber wherein the nanofiber material has anomalous morphologies(e.g., crystalline domains in a substantially amorphous nanofiber—suchcrystalline domains may increase fracturing and brittleness of thenanofiber), and the like. In some embodiments, there are about 1, about5, about 10, about 50, about 100, and the like defects per linear mm ofnanofiber. In some embodiments, there are at most about 1, at most about5, at most about 10, at most about 50, at most about 100, and the likedefects per linear mm of nanofiber. In other embodiments, the nanofibershave fewer defects and/or voids, wherein the number of defects and/orvoids in the nanofiber is in comparison to a nanofiber not produced bythe methods of the disclosure (for example with a low loading ofprecursor). In certain embodiments, high loading of precursor, relativeto polymer loading, in the fluid stock and/or precursor/electrospunnanofibers, facilitates and/or provides such high quality nanofibers.

Provided in various embodiments herein are carbonaceous nanofiberscomprising high metal and carbon content (e.g., carbonaceous nanofiberscomprising a carbon matrix and domains of metal or metal carbidenanofibers). In some embodiments, nanofibers provided herein comprise atleast 99%, at least 98%, at least 97%, at least 96%, at least 95%, atleast 90%, at least 80%, or the like of metal and carbon, when takentogether, by mass (e.g., elemental mass). In some embodiments,carbonaceous nanofibers provided herein comprise at least 50%, at least60%, at least 70%, or at least 75% metal by mass (e.g., elemental mass).

In some embodiments, nanofibers provided herein comprise less than 5%oxygen by mass. In certain embodiments, nanofibers provided hereincomprise less than 3% oxygen by mass. In specific embodiments,nanofibers provided herein comprise less than 2% oxygen by mass. In morespecific embodiments, nanofibers provided herein comprise less than 2%oxygen by mass. In still more specific embodiments, nanofibers providedherein comprise less than 0.5% oxygen by mass.

Provided in certain embodiments herein are nanostructures comprisinghigh metal, oxygen and optionally carbon content (e.g., carbonaceousnanofibers comprising a carbon matrix and domains of metal oxide). Insome embodiments, nanostructures provided herein comprise at least 99%,at least 98%, at least 97%, at least 96%, at least 95%, at least 90%, atleast 80%, or the like of metal, oxygen and carbon, when taken together,by mass (e.g., elemental mass). In more specific embodiments,nanostructures provided herein comprise at least 99%, at least 98%, atleast 97%, at least 96%, at least 95%, at least 90%, at least 80%, orthe like of metal and oxygen, when taken together, by mass (e.g.,elemental mass). In some embodiments, carbonaceous nanofibers providedherein comprise at least 20%, at least 30%, at least 40%, or at least50% metal by mass (e.g., elemental mass). In some embodiments,nanostructures provided herein comprise at least 50%, at least 60%, atleast 70%, or at least 75% metal oxide by mass (e.g., elemental mass).

In some embodiments, nanostructures provided herein comprise acontinuous matrix of a metal component described herein (e.g., metal,metal oxide, ceramic, metal carbide, or the like). In some specificembodiments, the continuous matrix is a continuous crystalline matrix.In other specific embodiments, the continuous matrix is a continuousamorphous matrix. In some embodiments, a continuous matrix of ananostructure described herein is continuous along a substantial portionof the nanostructure (e.g., along the length—longest dimension—of thenanostructure). In some embodiments, the continuous matrix is foundalong at least 50%, at least 60%, at least 70%, at least 80%, at least90%, at least 95%, at least 98%, or at least 99% the length of thenanostructure (e.g., on average for a plurality of nanostructures). Insome instances, the continuous matrix runs along at least 50% the lengthof the nanostructure (e.g., on average for populations of nanofibers).In specific instances, the continuous matrix runs along at least 70% thelength (e.g., on average) of the nanostructure(s). In more specificinstances, the continuous matrix runs along at least 80% the length(e.g., on average) of the nanostructure (s). In still more specificembodiments, the continuous matrix runs along at least 90% of the length(e.g., on average) of the nanostructure (s). In yet more specificembodiments, the continuous matrix runs along at least 95% of the length(e.g., on average) of the nanostructure (s).

FIGS. 13A-13C illustrates the XRD data for exemplary nanostructuresprovided herein. Panels A, C, D, E, and I illustrate XRD data forcrystalline nanofibers of metal nanostructures. Panels B, F, G, and Hillustrate XRD data for crystalline nanofibers of metal oxidenanostructures. Panels O, P, Q, and R illustrate XRD data for exemplarycrystalline metal alloy nanostructures. Panels J, K, L, M, and N (withno peaks for amorphous alumina) illustrate XRD data for exemplarynanocomposite nanostructures.

Metal Component

Provided herein are nanostructures and processes of preparing suchnanostructures, wherein the nanostructures comprise at least one metalcomponent. In some embodiments, the at least one metal componentcomprises a single metal component. In other embodiments, the at leastone metal component(s) comprise two or more metal components (e.g., acomposite material). In addition, in some embodiments, each metalcomponent independently comprises one or more metal type (e.g., anexample of a metal component comprising two or more metal types is ametal-metal alloy) (a “metal type” may be a specific metal in a zerooxidation state and/or an oxidation state greater than zero). Thus, insome instances, provided herein are metal components comprising a singlemetal type, but in further or other embodiments, provided herein aremetal components comprising two or more metal type. In some instances, ananostructure comprises at least two metal components, e.g., one ofwhich comprises a single metal type, and a second comprises two or moremetal types.

In certain embodiments, a nanostructure provided herein comprises atleast one metal component. In various embodiments, the at least onemetal component comprises metal material comprising a single metal withan oxidation state of zero (e.g., Fe, Ti, Al, Cu, Co, Ni, Si, etc.), ora single metal with an oxidation state of greater than zero (e.g., ametal oxide, such as titania or zirconia; a metal carbide, such as ironcarbide, silicon carbide, titanium carbide; or the like). In otherembodiments, the at least one metal component comprises metal materialcomprising at least two metals with an oxidation state of zero (e.g.,Fe, Ti, Al, Cu, Co, Ni, Si, etc.), or at least two metals with anoxidation state of greater than zero (e.g., khamrabaevite—(Ti,V,Fe)C).In some instances, such metal components comprising at least two metalsare alloys. Exemplary metal components comprising two or more components(e.g., two or more metals) include, by way of non-limiting example,CdSe, CdTe, PbSe, PbTe, FeNi (perm alloy), Fe—Pt intermetallic compound,stainless steel, Pt—Pb, Pt—Pd, Pt—Bi, Pd—Cu, and Pd—Hf. In otherembodiments, the at least one metal component comprises metal materialcomprising at least one metal with an oxidation state of zero (e.g., Fe,Ti, Al, Cu, Co, Ni, etc.), and at least one metal with an oxidationstate of greater than zero.

In some embodiments, the metal component is or comprises at least onemetalloid component. In various embodiments, the at least one metalcomponent comprises metalloid material comprising a single metal with anoxidation state of zero (e.g. Si), or a single metalloid with anoxidation state of greater than zero (e.g., SiO₂, SiC). In otherembodiments, the at least one metal component comprises metal materialcomprising at least two metalloids with an oxidation state of zero, orat least two metalloids with an oxidation state of greater than zero.

In some embodiments, a nanostructure comprises at least one metalcomponent. In yet other embodiments, the at least one metal componentcomprises metal material comprising at least one metal with an oxidationstate of zero (e.g., Fe, Ti, Al, Cu, Co, Ni, etc.), and at least onemetal with an oxidation state of greater than zero (e.g., a metal oxide,a metal carbide, or the like).

In various embodiments, a metal component (or metal reagent component)provided herein comprises any suitable metal (e.g., in a zero or greaterthan zero oxidation state), including a transition metal, alkali metal,alkaline earth metal, post-transition metal, lanthanide, or actinide. Incertain embodiments, the metal is a transition metal. In someembodiments, the metal is a period IV transition metal. In certainembodiments, the metal is a period V transition metal. In someembodiments, the metal is a group XIII metal. In certain embodiments,the metal is a group XIV metal. In various embodiments, transitionmetals include: scandium (Sc), titanium (Ti), vanadium (V), chromium(Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo),technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver(Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium(Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg),rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), andhasium (Hs). Suitable alkali metals include: lithium (Li), sodium (Na),potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr). Suitablealkaline earth metals include: beryllium (Be), magnesium (Mg), calcium(Ca), strontium (Sr), barium (Ba), and radium (Ra). Suitablepost-transition metals include: aluminum (Al), gallium (Ga), indium(In), tin (Sn), thallium (Tl), lead (Pb), and bismuth (Bi). Suitablelanthanides include the elements with atomic number 57 to 71 on theperiodic table. Suitable actinides include the elements with atomicnumber 89 to 103 on the periodic table. In some embodiments, the metalis a metalloid, such as, germanium (Ge), antimony (Sb) and polonium(Po), or silicon (Si). It is to be understood that metal componentsdescribed herein are intended to include metalloid components. In someembodiments, the metal component is not an oxide of silicon (e.g., SiO₂or SiTiO₃). In other embodiments, the metal component is not an oxide oftitanium (e.g., TiO₂ or SiTiO₄). In yet other embodiments, the metalcomponent is not a ceramic.

Such metals are optionally present in the metal component(s) of thenanostructure in an oxidation state of zero (generally referred toherein as a “elemental metal” or “elemental metalloid”), greater thanzero, or a combination thereof. Oxidations states of greater than zeroinclude metal oxides, metal carbides, and the like. In specificembodiments, the metal component of a nanostructure provided hereincomprises a metal oxide. In more specific embodiments, the metal oxideis a ceramic, such as alumina, silica, titania, zirconia, or the like.Exemplary metal components comprising a metal oxide include, by way ofnon-limiting example, Al₂O₃, ZrO₂, Fe₂O₃, CuO, NiO, ZnO, CdO, SiO₂,TiO₂, V₂O₅, VO₂, Fe₃O₄, SnO, SnO₂, CoO, CoO₂, CO₃O₄, HfO₂, BaTiO₃,SrTiO₃, Ba_(0.55)Sr_(0.45)TiO₃, and the like.

In certain embodiments, at least one of the metal components is amaterial of formula (I):

M_(x)L_(y)  (I)

wherein M is one or more metal and L is one or more of B, C, N, O, P, S,and/or Se, x is an integer of greater than 0, y is an integer, and z is2-4.

In some embodiments, nanostructures described herein comprise at leastone of the metal component of formula (Ia):

M¹ _(a)M² _(b)M³ _(c)M⁴ _(d)L¹ _(g)L² _(h)  (Ia)

In specific embodiments, each of M¹, M², M³, and M⁴ is independentlyselected from a metal. In some embodiments, each of L¹ and L² isindependently selected from B, C, N, O, P, S, or Se. In someembodiments, each of a, b, c, and d are independently selected from0-25, the sum of a, b, c, and d is an integer greater than 0, each of gand h is independently selected from 0-10, an the sum of g and h is aninteger 0-20. In specific embodiments, g and h are 0. In someembodiments, L¹ is O and h is 0. In some embodiments, L¹ is B, C, or S,and h is 0. In specific embodiments, each of M¹, M², M³, and M⁴ areindependently selected from Fe, Ti, Si, Ag, Cu, Ni, Co, Au, Al, Zr, Li,Mg, Ca, Hf, Mn, Ru, Rh, Zn, Cd, Sn, Ge. In more specific embodiments,each of M¹, M², M³, and M⁴ are independently selected from Fe, Ti, Ag,Cu, Ni, Co, Au, Zr, Li, Mg, Ca, Hf, Mn, Ru, Rh, Zn, Cd, Sn, Ge.

Nanocomposite

In some embodiments, the nanostructure provided herein is ananocomposite nanostructure. As described herein, a nanocompositenanostructure is a material comprising at least two differentcomponents, at least one of which is a metal component as describedherein. In some embodiments, the second component is a second metalcomponent. Such nanocomposite nanostructures may also be described ascomposite nanostructures or hybrid nanostructures. FIG. 9 illustrates anexemplary nanostructure nanocomposite 900 comprising (i) discretedomains of metal component 901, and (ii) a continuous matrix material902 (which may comprise a second metal component or another material,such as amorphous carbon). As illustrated in the cross-sectional view903, the discrete domains of metal component 904 may penetrate into thecore 905 of the nanostructure. In some instances, the nanostructurescomprise metal component on the surface of the nanostructure. And insome instances, the nanostructures comprise or further comprise discretedomains of metal component completely embedded within the core matrixmaterial.

In some embodiments, hybrid nanostructures comprise (i) a continuousmatrix material comprising a first component, and (ii) a plurality ofisolated domains comprising a second component. In some embodiments, thecontinuous matrix is crystalline or amorphous. In certain embodiments,the isolated domains comprise nanoparticles (e.g., comprising a metalcomponent). In specific embodiments, the first (continuous matrix)component is any metal component described herein. In others, it is not.In some embodiments, the first (continuous matrix) component is carbon(e.g., amorphous carbon). In specific embodiments, the second componentis any metal component described herein. In certain embodiments, acontinuous matrix comprises a single material (and, in some instances, asimilar morphology) along a significant portion of the nanostructure.For example a continuous matrix within a nanostructure is continuousalong at least 50% of the length of the nanostructure (i.e., the longestdimensions of the nanostructure). In more specific embodiments, thecontinuous matrix runs along at least 70% of the length of thenanostructure. In still more specific embodiments, the continuous matrixruns along at least 80% of the length of the nanostructure. In yet morespecific embodiments, the continuous matrix runs along at least 90% ofthe length of the nanostructure. In specific embodiments, the continuousmatrix runs along at least 95% of the length of the nanostructure. Inmore specific embodiments, the continuous matrix runs along at least 98%of the length of the nanostructure. In yet more specific embodiments,the continuous matrix runs along at least 99% of the length of thenanostructure.

In certain embodiments, hybrid nanostructures comprise (i) a corecomprising a first material; and (ii) a sheath comprising a secondmaterial, wherein the sheath material is layered upon and/or at leastpartially coats or covers the core material. Additional layers arelayered on top of the sheath. Each optional layer may comprise furthercomponents, or components similar to those found in the core and/orsheath. In some instances, the hybrid nanostructure comprises a core andat least two layers (one of which is the sheath), wherein the core andtwo layers all comprise different materials. In other embodiments, thehybrid nanostructure comprises a core and at least two layers, whereinthe core and outer layer are the same material.

In some embodiments, such hybrid nanostructures are prepared byelectrospinning a first fluid stock and a second fluid stock (andoptional additional fluid stock(s)) about a common axis (i.e., co-axialelectrospinning). For additional disclosure on common axialelectrospinning, see U.S. patent application Ser. No. 13/451,960, whichis hereby incorporated herein by reference in its entirety, and,specifically, for such disclosure. In some embodiments, the first layer(core) comprises an elemental or alloy metal. In some embodiments thesecond layer (sheath) comprises an elemental or alloy metal. In variousembodiments, the hybrid nanofiber is elemental or alloymetal-on-elemental metal, ceramic-on-elemental or alloy metal,ceramic-on-ceramic, or an elemental or alloy metal-on-ceramic. In someembodiments, the hybrid nanofiber has at least 3 components.

Additional Components

In certain embodiments, any nanostructure described herein optionallyfurther comprises one or more additional component (i.e., in addition tothe at least one metal component). For example, a nanostructuredescribed herein may optionally comprise a continuous carbon matrix. Insome embodiments, other materials may be present, such as organicmaterials, organic components, reactive compounds, additive, or thelike.

In certain embodiments, a nanostructure or plurality of nanostructuresprovided herein comprises, on average, less than 20 wt. % organicmaterial. In specific embodiments, a nanostructure provided hereincomprises, on average, less than 10 wt. % organic material. In morespecific embodiments, a nanostructure provided herein comprises, onaverage, less than 5 wt. % organic material. In still more specificembodiments, a nanostructure provided herein comprises, on average, lessthan 2 wt. % organic material. In yet more specific embodiments, ananostructure provided herein comprises, on average, less than 1 wt. %organic material. In some embodiments, a nanostructure provided hereincomprises, on average, less than 50 wt. % organic material, less than 30wt. % organic material, less than 15 wt. % organic material, less than 3wt. % organic material, less than 0.5 wt. % organic material, less than0.1 wt. % organic material.

In certain embodiments, a nanostructure or plurality of nanostructure(s)provided herein comprises on average less than 20 elemental wt. %carbon. In specific embodiments, a nanostructure provided hereincomprises, on average, less than 10 elemental wt. % carbon. In morespecific embodiments, a nanostructure provided herein comprises, onaverage, less than 5 elemental wt. % carbon. In still more specificembodiments, a nanostructure provided herein comprises, on average, lessthan 2 elemental wt. % carbon. In yet more specific embodiments, ananostructure provided herein comprises, on average, less than 1elemental wt. % carbon. In some embodiments, a nanostructure providedherein comprises, on average, less than 50 elemental wt. % carbon, lessthan 30 elemental wt. % carbon, less than 15 elemental wt. % carbon,less than 3 elemental wt. % carbon, less than 0.5 elemental wt. %carbon, less than 0.1 elemental wt. % carbon.

Nano Structures

In certain embodiments, nanostructures provided herein comprisenanofibers, nanofiber fragments, or a combination thereof. In someaspects, described herein are nanostructures, nanofibers (or fragmentsthereof), or composite materials comprising the same having novel orimproved properties. In various embodiments, these nanostructures ornanofibers (or fragments thereof) have certain dimensions, aspectratios, specific surface areas, porosities, conductivities,flexibilities, and the like that are beyond what was previouslyachievable.

In some embodiments, provided herein are the nanostructures ornanofibers (or fragments thereof) having an (e.g., mean or median)aspect ratio of more than 20. In specific embodiments, nanostructures ornanofibers (or fragments thereof) provided herein an (e.g., mean ormedian) aspect ratio of more than 40. In more specific embodiments,nanostructures or nanofibers (or fragments thereof) provided herein an(e.g., mean or median) aspect ratio of more than 50. In still morespecific embodiments, nanostructures or nanofibers (or fragmentsthereof) provided herein an (e.g., mean or median) aspect ratio of morethan 100. In yet more specific embodiments, nanostructures or nanofibers(or fragments thereof) provided herein an (e.g., mean or median) aspectratio of more than 200. In more specific embodiments, nanostructures ornanofibers (or fragments thereof) provided herein an (e.g., mean ormedian) aspect ratio of more than 400. In more specific embodiments,nanostructures or nanofibers (or fragments thereof) provided herein an(e.g., mean or median) aspect ratio of more than 500. In yet morespecific embodiments, nanostructures or nanofibers (or fragmentsthereof) provided herein an (e.g., mean or median) aspect ratio of morethan 1000. The nanostructure have any suitable aspect ratio(length/diameter). In some embodiments, the nanostructures have (e.g.,mean or median) an aspect ratio of about 10, about 10², or about 10³,about 10⁴, about 10⁵, about 10⁶, about 10⁷, about 10⁸, about 10⁹, about10¹⁰, about 10¹¹, about 10¹², and the like. In some embodiments thenanostructures have an aspect ratio (e.g., mean or median) of at least10, at least 10², or at least 10³. In specific embodiments, thenanostructure have an aspect ratio (e.g., mean or median) of at least10⁴, at least 10⁵, at least 10⁶, at least 10⁷, at least 10⁸, at least10⁹, at least 10¹⁰, at least 10¹¹, at least 10¹², and the like. In someembodiments, the nanostructure is of substantially infinite length andhas an aspect ratio of substantially infinity.

Nanostructures provided herein may have any suitable diameter (e.g., asdetermined by SEM, TEM, or any other suitable method) (e.g., the mostnarrow, or most narrow non-defect, dimension of the nanostructure). Insome embodiments, nanostructures provided herein have (e.g., on average)a diameter of about 20 nm, about 30 nm, about 40 nm, about 50 nm, about60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm, about 130nm, about 150 nm, about 200 nm, about 250 nm, about 300 nm, about 400nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900nm, about 1,000 nm, about 1,500 nm, about 2,000 nm and the like. In someembodiments, nanostructures provided herein have (e.g., on average) adiameter of at most 20 nm, at most 30 nm, at most 40 nm, at most 50 nm,at most 60 nm, at most 70 nm, at most 80 nm, at most 90 nm, at most 100nm, at most 130 nm, at most 150 nm, at most 200 nm, at most 250 nm, atmost 300 nm, at most 400 nm, at most 500 nm, at most 600 nm, at most 700nm, at most 800 nm, at most 900 nm, at most 1,000 nm, at most 1,500 nm,at most 2,000 nm and the like. In certain embodiments, nanostructuresprovided herein have (e.g., on average) a diameter of between about 50nm and about 300 nm, between about 50 nm and about 150 nm, between about100 nm and about 400 nm, between about 100 nm and about 200 nm, betweenabout 500 nm and about 800 nm, between about 60 nm and about 900 nm, andthe like. In specific embodiments, nanostructures provided herein have(e.g., on average) a diameter of less than 500 nm. In more specificembodiments, nanostructures provided herein have (e.g., on average) adiameter of less than 250 nm. In specific embodiments, nanostructuresprovided herein have a (e.g., average) diameter of 100 nm to 1000 nm. Insome embodiments, nanostructures provided herein have a (e.g., average)diameter of 500 nm or less. In some embodiments, nanostructures providedherein have a (e.g., average) diameter of 400 nm or less. In someembodiments, nanostructures provided herein have a (e.g., average)diameter of 200 nm to 500 nm. In other specific embodiments, precursornanofibers described herein have a (e.g., average) diameter of less than2000 nm. In more specific embodiments, electrospun precursor nanofibersdescribed herein have a (e.g., average) diameter of 300 nm to 1500 nm.

The nanostructures have any suitable length (e.g., as determined bymicroscopy, such as SEM or TEM, or any other suitable technique). Insome instances, a given plurality of nanostructures comprisenanostructures that have a distribution of structures of variouslengths. In some embodiments, certain structures of a population exceedor fall short of the average length. In some embodiments, nanostructuresprovided herein have an average length of about 20 μm, about 50 μm,about 100 μm, about 500 μm, about 1,000 μm, about 5,000 μm, about 10,000μm, about 50,000 μm, about 100,000 μm, about 500,000 μm, and the like.In some embodiments, the nanofiber has an average length of at leastabout 20 μm, at least about 50 μm, at least about 100 μm, at least about500 μm, at least about 1,000 μm, at least about 5,000 μm, at least about10,000 μm, at least about 50,000 μm, at least about 100,000 μm, at leastabout 500,000 μm, and the like. In some embodiments, the nanofiber hasan average length of less than about 0.2 μm, less than about 0.5 μm,less than about 1 μm, less than about 2 μm, less than about 3 μm, lessthan about 5 μm, less than about 10 μm, less than about 20 μm, less thanabout 50 μm, less than about 100 μm, less than about 500 μm, less thanabout 1,000 μm, less than about 5,000 μm, less than about 10,000 μm,less than about 50,000 μm, less than about 100,000 μm, less than about500,000 μm, and the like.

The nanostructures provided herein have any suitable specific surfacearea (surface area divided by mass (or volume)). In some embodiments,the specific surface area of nanostructures provided herein is at least0.1 m²/g, at least 1 m²/g, at least 5 m²/g, at least 10 m²/g, at least50 m²/g, at least 100 m²/g, at least 200 m²/g, at least 500 m²/g, atleast 1,000 m²/g, at least 1,500 m²/g, at least 2,000 m²/g, or the like.

The nanostructures have any suitable porosity. In certain instances, ahigh surface area nanostructure, such as one having high porosity,provides an additive material that, when combined to form a composite,provides a material having minimal density distortions therein. In someembodiments, the porosity is about 1%, about 2%, about 4%, about 6%,about 8%, about 10%, about 15%, about 20%, about 25%, about 30%, about40%, about 50%, about 60%, about 70% and the like. In some embodiments,the porosity is at most 1%, at most 2%, at most 4%, at most 6%, at most8%, at most 10%, at most 15%, at most 20%, at most 25%, at most 30%, atmost 40%, at most 50%, at most 60%, at most 70% and the like. In someembodiments, the porosity is at least 1%, at least 2%, at least 4%, atleast 6%, at least 8%, at least 10%, at least 15%, at least 20%, atleast 25%, at least 30%, at least 40%, at least 50%, at least 60%, atleast 70% and the like. In some embodiments, the porosity is betweenabout 1% and 10%, between about 10% and 50%, between about 20% and 30%,between about 30% and 70%, between about 1% and 50%, between about 5%and 20%, and the like. In certain instances, porosity is the void amountof the nanostructure divided by the theoretical volume of thenanostructure. In specific instances, porosity is determined bymeasuring the volume displacement caused by the nanofiber in a fluid andcomparing it the theoretical volume of the nanostructure (e.g.,π·radius²·length).

Methods for measuring the diameter, aspect ratio, or other dimensionalcharacteristic of a nanostructure or nanofiber described herein mayinclude any suitable method. Such methods include, but are not limitedto microscopy, optionally transmission electron microscopy (“TEM”) orscanning electron microscopy (“SEM”). Surface area may be calculated bymeasuring the diameter and length of nanofiber in the sample andapplying the equation for the surface area of a cylinder (i.e., 2 timespi times half of the diameter of the nanofiber times the sum of thelength of the nanofiber and half of the diameter of the nanofiber).Surface area may also be measured by physical or chemical methods, forexample by the Brunauer-Emmett, and Teller (BET) method where thedifference between physisorption and desorption of inert gas isutilized.

In certain embodiments, nanofiber nanostructures are produced bythermally treating precursor nanofibers from an aqueous fluid stockcomprising polymer and metal precursor.

In some embodiments, nanostructures described herein that have anaverage length of at least 750 microns. In more specific embodiments,the nanostructures have an average length of at least 1 mm. In stillmore specific embodiments, the nanostructures have an average length ofat least 1.5 mm, or at least 2 mm. In some embodiments, thenanostructures comprise a continuous metal, metal oxide, metal carbide,or ceramic matrix and have an average length of at least 1 mm (e.g., atleast 1.5 mm, at least 2 mm, or at least 5 mm). In certain embodiments,the nanostructures have an average aspect ratio of at least 1,000. Inspecific embodiments, the nanostructures have an average aspect ratio ofat least 10,000. In still more specific embodiments, the nanostructureshave an average aspect ratio of at least 25,000 (e.g., at least 50,000,at least 100,000, or the like). In some embodiments, the nanostructurescomprise a continuous metal, metal oxide, metal carbide, or ceramicmatrix and have an average aspect ratio of at least 10,000 (e.g., atleast 25,000 or at least 100,000). In some embodiments, thenanostructures comprise a continuous metal, metal oxide, metal carbide,or ceramic matrix and have an average aspect ratio of at least 10,000(e.g., at least 25,000 or at least 100,000) and an average length of atleast 1 mm (e.g., at least 1.5 mm, at least 2 mm, or at least 5 mm).

Nanostructure Properties

In certain embodiments, nanostructures provided herein have improvedperformance over other nano-material additives. In some instances,Young's modulus, fracture toughness, ultimate strength, electricalconductivity, thermal conductivity, flexibility, and/or othercharacteristics of the nanostructures described herein (and/or theircomposite materials) are improved over other nanostructures of the samematerial and/or over the bulk/sheet form of the same material. Table 1illustrates the physical properties of certain nanostructures providedherein and the physical properties of bulk materials having similarstructure.

TABLE 1 Youngs Ultimate Electrical Modulus Fracture StrengthConductivity (GPa) Toughness (MPa) (log(S/m)) Material nano bulk (MPa ·m½) nano bulk nano bulk SiO₂ 79 80 0.71 41 33 — — (amorph) ZrO₂ 818 2102.15 2612 1900 — — Cu 608 117 4.12 191 70 6.6 7.4 SiC 1030 450 3.88 81203440 2.2 4.0

In some embodiments, nanostructures described herein have improvedYoung's modulus over similar materials in other nanostructure or bulkforms. In some instances, provided herein are nanostructures having amean or median nanofiber Young's modulus-to-diameter ratio of at least0.1 GPa/nm. In certain instances, provided herein are nanostructureshaving a mean or median nanofiber Young's modulus-to-diameter ratio ofat least 0.13 GPa/nm. In specific instances, provided herein arenanostructures having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 0.15 GPa/nm. In more specificinstances, provided herein are nanostructures having a mean or mediannanofiber Young's modulus-to-diameter ratio of at least 0.18 GPa/nm. Instill more specific instances, provided herein are nanostructures havinga mean or median nanofiber Young's modulus-to-diameter ratio of at least0.2 GPa/nm. In yet more specific instances, provided herein arenanostructures having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 0.25 GPa/nm. In specificinstances, provided herein are nanostructures having a mean or mediannanofiber Young's modulus-to-diameter ratio of at least 0.3 GPa/nm. Insome instances, provided herein are nanostructures having a mean ormedian nanofiber Young's modulus-to-diameter ratio of at least 0.05GPa/nm or at least 0.5 GPa/nm.

In some embodiments, provided herein are nanostructures having a mean ormedian nanofiber Young's modulus-to-bulk Young's modulus of the metalcomponent of at least 0.8:1. In specific embodiments, nanostructuresprovided herein have a mean or median nanofiber Young's modulus-to-bulkYoung's modulus of the metal component of at least 1:1. In more specificembodiments, nanostructures provided herein have a mean or mediannanofiber Young's modulus-to-bulk Young's modulus of the metal componentof at least 3:2. In still more specific embodiments, nanostructuresprovided herein have a mean or median nanofiber Young's modulus-to-bulkYoung's modulus of the metal component of at least 2:1. In still morespecific embodiments, nanostructures provided herein have a mean ormedian nanofiber Young's modulus-to-bulk Young's modulus of the metalcomponent of at least 3:1. In still more specific embodiments,nanostructures provided herein have a mean or median nanofiber Young'smodulus-to-bulk Young's modulus of the metal component of at least 4:1.Generally, comparisons to such bulk material involve comparisons ofcrystalline nanostructures to crystalline bulk material and amorphousnanostructures to amorphous bulk material.

In certain embodiments, nanostructures described herein have improvedfracture toughness over similar materials in other nanostructure or bulkforms. In some instances, provided herein are nanostructures having amean or median nanofiber fracture toughness-to-diameter ratio of atleast 0.002 MPa·m^(1/2)/nm. In some instances, provided herein arenanostructures having a mean or median nanofiber fracturetoughness-to-diameter ratio of at least 0.003 MPa·m^(1/2)/nm. In someinstances, provided herein are nanostructures having a mean or mediannanofiber fracture toughness-to-diameter ratio of at least 0.005MPa·m^(1/2)/nm. In some instances, provided herein are nanostructureshaving a mean or median nanofiber fracture toughness-to-diameter ratioof at least 0.007 MPa·m^(1/2)/nm. In some instances, provided herein arenanostructures having a mean or median nanofiber fracturetoughness-to-diameter ratio of at least 0.01 MPa·m^(1/2)/nm. In certainembodiments, nanostructures provided herein have a mean or mediannanofiber fracture toughness of at least 0.5 MPa·m^(1/2). In certainembodiments, nanostructures provided herein have a mean or mediannanofiber fracture toughness of at least 0.7 MPa·m^(1/2). In certainembodiments, nanostructures provided herein have a mean or mediannanofiber fracture toughness of at least 0.9 MPa·m^(1/2). In certainembodiments, nanostructures provided herein have a mean or mediannanofiber fracture toughness of at least 1 MPa·m^(1/2). In certainembodiments, nanostructures provided herein have a mean or mediannanofiber fracture toughness of at least 2 MPa·m^(1/2). In certainembodiments, nanostructures provided herein have a mean or mediannanofiber fracture toughness of at least 3 MPa·m^(1/2). In certainembodiments, nanostructures provided herein have a mean or mediannanofiber fracture toughness of at least 5 MPa·m^(1/2).

In certain embodiments, nanostructures described herein have improvedultimate strength over similar materials in other nanostructure or bulkforms. In certain embodiments, nanostructures provided herein have amean or median nanofiber ultimate strength-to-bulk ultimate strength ofthe metal component of at least 0.8:1. In some embodiments,nanostructures provided herein have a mean or median nanofiber ultimatestrength-to-bulk ultimate strength of the metal component of at least1:1. In specific embodiments, nanostructures provided herein have a meanor median nanofiber ultimate strength-to-bulk ultimate strength of themetal component of at least 1.2:1. In more specific embodiments,nanostructures provided herein have a mean or median nanofiber ultimatestrength-to-bulk ultimate strength of the metal component of at least1.5:1. In still more specific embodiments, nanostructures providedherein have a mean or median nanofiber ultimate strength-to-bulkultimate strength of the metal component of at least 2:1. In still morespecific embodiments, nanostructures provided herein have a mean ormedian nanofiber ultimate strength-to-bulk ultimate strength of themetal component of at least 3:1.

In some embodiments, nanostructures provided herein have (an average)electrical conductivity of at least 5%, at least 10%, at least 20%, atleast 30%, at least 40%, at least 50%, at least 60%, at least 70%, atleast 80%, at least 90%, at least 95%, at least 100%, at least 110%, atleast 120%, at least 130%, at least 150%, or at least 200% when comparedwith the conductivity of the bulk material (e.g., when formed into asheet). In some embodiments, the conductivity is at least 1 S/cm, atleast 10 S/cm, at least 100 S/cm, at least 10³ S/cm, at least 10⁴ S/cm,at least 10⁵ S/cm, at least 10⁶ S/cm, at least 10⁷ S/cm, at least 10⁸S/cm, and the like. In some embodiments, the conductivity is betweenabout 1 S/cm and 10 S/cm, between about 10 S/cm and 100 S/cm, betweenabout 100 S/cm and 1,000 S/cm, between about 1,000 S/cm and 10⁴ S/cm,between about 10⁴ S/cm and 10⁵ S/cm, between about 10⁵ S/cm and 10⁶S/cm, between about 10⁶ S/cm and 10⁷ S/cm, between about 10⁷ S/cm and10⁸ S/cm, between about 10⁵ S/cm and 10⁸ S/cm, and the like. Forexample, FIG. 12 illustrates the electrical conductivity of certainnanostructures described herein relative to their corresponding bulkmaterial.

In some embodiments, the nanostructures or composite comprisingnanostructures of the present disclosure are flexible. In someinstances, flexible nanofibers are advantageous in certain applications.In some instances, flexibility is quantified by the Young's modulus,which is the slope of the initial linear portion of a stress-straincurve. The Young's modulus has units of pressure, such as mega Pascals(MPa). In some embodiments, flexibility is different along differentdirections of the material, so may be reported with respect to a certaindirection, or is reported as an average value. The nanostructures haveany suitable flexibility. In some embodiments, the nanostructures has aYoung's modulus of at least 10 MPa, at least 100 MPa, at least 250 MPa,at least 500 MPa, at least 1,000 MPa, at least 4,000 MPa, at least 6,000MPa, at least 8,000 MPa, or the like.

In some embodiments, provided herein are reinforcing additivescomprising nanofiber nanostructures having the matrix material describedand anyone one or more of characteristics set forth in Table 2:

TABLE 2 Fracture Continuous Youngs Toughness Ultimate Electrical MatrixModulus (MPa · Strength Conductivity Material (GPa) m½) (MPa) (log(S/m))amorphous ≧50 ≧75 ≧0.7 ≧35 ≧40 — — metal oxide or ceramic crystalline≧500 ≧750 ≧2 ≧2000 ≧2500 — — ceramic metal ≧200 ≧500 ≧4 ≧100 ≧150 ≧3 ≧5metal ≧500 ≧1000 ≧3 ≧4000 ≧8000 ≧1 ≧2 carbide

Metals

In certain embodiments, provided herein are nanostructures (e.g.,nanofiber nanostructures) comprising one or more zero oxidation statemetal (a metal described herein, generally refers to a zero oxidationstate metal, unless otherwise stated). In specific embodiments, thenanostructures comprise a single zero oxidation state metal. In general,the metal may be any suitable metal, such as one of those describedherein. In some embodiments, the metal (i.e., zero oxidation statemetal) is Fe, Ti, Si, Ag, Cu, Ni, Co, Au, Al, Zr, Hf, Mn, Ru, Rh, Zn,Cd, Sn, or Ge. In specific embodiments, the nanostructures comprise zerooxidation state metal. In more specific embodiments, the one or morezero oxidation state metal is nickel (Ni). In other embodiments, the oneor more zero oxidation state metal is copper (Cu). In still otherembodiments, the one or more zero oxidation state metal is silver (Ag).In yet other embodiments, the one or more zero oxidation state metal isiron (Fe). In still other embodiments, the one or more zero oxidationstate metal is lead (Pb). In yet other embodiments, the one or more zerooxidation state metal is cobalt (Co). In other embodiments, thenanostructures comprise zero oxidation state metalloid. In specificembodiments, the zero oxidation state metalloid is silicon.

In some embodiments, the one or more zero oxidation state metal is ametal alloy. In specific embodiments, the metal alloy is a carbon alloy,a selenium alloy, a metal-metal alloy, a metal-metal oxide alloy, atellurium alloy, or the like. In general, the alloy may comprise anysuitable metal, in combination with a second component, such as carbon,selenium, tellurium, a non-metal, additional metal(s), metal oxides, orany other suitable component. In specific embodiments, the metal alloycomprises Fe, Ti, Si, Ag, Cu, Ni, Co, Au, Al, Zr, Li, Mg, Ca, Hf, Mn,Ru, Rh, Zn, Cd, Sn, Ge, or any combination thereof.

Such structures may have any of the performance characteristicsdescribed herein. Exemplary performance characteristics of metalnanostructures described herein are described throughout this disclosureand below.

In certain embodiments, the nanostructures comprise (e.g., on average)at least 50 wt. % zero oxidation state metal. In specific embodiments,the nanostructures comprise (e.g., on average) at least 60 wt. % zerooxidation state metal. In more specific embodiments, the nanostructurescomprise (e.g., on average) at least 75 wt. % zero oxidation statemetal. In still more specific embodiments, the nanostructures comprise(e.g., on average) at least 90 wt. % zero oxidation state metal. In yetmore specific embodiments, the nanostructures comprise (e.g., onaverage) at least 95 wt. % zero oxidation state metal. In specificembodiments, the nanostructures comprise (e.g., on average) at least 98wt. % zero oxidation state metal. In more specific embodiments, thenanostructures comprise (e.g., on average) at least 99 wt. % zerooxidation state metal.

In certain embodiments, the nanostructures comprise (e.g., on average)least 50 elemental wt. % metal, when taken together. In more specificembodiments, metal constitutes, on average, at least 60 elemental wt. %of the nanostructure(s). In still more specific embodiments, metalconstitutes, on average, at least 75 elemental wt. % of thenanostructure(s). In yet more specific embodiments, metal constitutes,on average, at least 80 elemental wt. % of the nanostructure(s). In morespecific embodiments, metal constitutes, on average, at least 90elemental wt. % of the nanostructure(s). In various embodiments, metalconstitutes, on average, at least 40 elemental wt. %, at least 70elemental wt. %, at least 85 elemental wt. %, at least 95 elemental wt.%, at least 97 elemental wt. %, at least 98 elemental wt. %, or at least99 elemental wt. % of the nanostructure(s).

In some embodiments, nanostructures provided herein have (an average)electrical conductivity of at least 50%, at least 60%, at least 70%, atleast 80%, at least 90%, at least 95%, at least 100%, at least 110%, atleast 120%, at least 130%, at least 150%, or at least 200% when comparedwith the conductivity of the bulk material (e.g., when formed into asheet).

In some embodiments, provided herein are nanostructures having a mean ormedian nanofiber Young's modulus-to-diameter ratio of at least 0.2GPa/nm. In specific instances, provided herein are nanostructures havinga mean or median nanofiber Young's modulus-to-diameter ratio of at least0.25 GPa/nm. In more specific instances, provided herein arenanostructures having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 0.3 GPa/nm. In still more specificinstances, provided herein are nanostructures having a mean or mediannanofiber Young's modulus-to-diameter ratio of at least 0.5 GPa/nm. Insome embodiments, provided herein are nanostructures having a mean ormedian nanofiber Young's modulus of at least 100 GPa. In specificinstances, provided herein are nanostructures having a mean or mediannanofiber Young's modulus of at least 200 GPa. In more specificinstances, provided herein are nanostructures having a mean or mediannanofiber Young's modulus of at least 300 GPa. In still more specificinstances, provided herein are nanostructures having a mean or mediannanofiber Young's modulus of at least 500 GPa.

In certain embodiments, nanostructures provided herein have a mean ormedian nanofiber ultimate strength-to-bulk ultimate strength of themetal component of at least 1:1. In more specific embodiments,nanostructures provided herein have a mean or median nanofiber ultimatestrength-to-bulk ultimate strength of the metal component of at least2:1.

Metal Oxides/Ceramics

In certain embodiments, provided herein are nanostructures (e.g.,nanofiber nanostructures) comprising one or more metal having anoxidation state of greater than zero. In specific embodiments, thenanostructures comprise a single metal component having an oxidationstate of greater than zero. In specific embodiments, the metal componentis a metal oxide (e.g., a ceramic). In general, the metal oxide may bean oxide of any suitable metal(s), metalloid(s), or combination thereof.Exemplary metals include those described herein. In some embodiments,the metal oxide is an oxide of Fe, Ti, Si, Ag, Cu, Ni, Co, Au, Al, Zr,Hf, Mn, Ru, Rh, Zn, Cd, Sn, Ge, or a combination thereof. In specificembodiments, the nanostructures comprise an oxidized metal. In morespecific embodiments, the oxidized metal is an oxide of nickel (Ni). Inother embodiments, the oxidized metal is an oxide of copper (Cu). Instill other embodiments, the oxidized metal is an oxide of zinc (Zn). Inyet other embodiments, the oxidized metal is an oxide of zirconium (Zr).In still other embodiments, the oxidized metal is an oxide of titanium(Ti). In yet other embodiments, the oxidized metal is an oxide of cobalt(Co). In yet other embodiments, the one or more zero oxidation statemetal is barium (Ba). In specific embodiments, the oxidized metalloid isan oxide of silicon (e.g., silica).

Such structures may have any of the performance characteristicsdescribed herein. Exemplary performance characteristics of metal oxide(e.g., ceramic) nanostructures described herein are described throughoutthis disclosure and below.

In certain embodiments, the metal oxide (e.g., ceramic) is in anamorphous state. In specific embodiments, nanostructures provided hereincomprise a continuous matrix of amorphous metal oxide (e.g., ceramic).For example a continuous matrix within a nanostructure is continuousalong at least 50% of the length of the nanostructure (i.e., the longestdimensions of the nanostructure). In more specific embodiments, thecontinuous matrix runs along at least 70% of the length of thenanostructure. In still more specific embodiments, the continuous matrixruns along at least 80% of the length of the nanostructure. In yet morespecific embodiments, the continuous matrix runs along at least 90% ofthe length of the nanostructure. In specific embodiments, the continuousmatrix runs along at least 95% of the length of the nanostructure. Inmore specific embodiments, the continuous matrix runs along at least 98%of the length of the nanostructure. In yet more specific embodiments,the continuous matrix runs along at least 99% of the length of thenanostructure.

In certain embodiments, the nanostructures comprise (e.g., on average)at least 50 wt. % metal oxide. In specific embodiments, thenanostructures comprise (e.g., on average) at least 60 wt. % metaloxide. In more specific embodiments, the nanostructures comprise (e.g.,on average) at least 75 wt. % metal oxide. In still more specificembodiments, the nanostructures comprise (e.g., on average) at least 90wt. % metal oxide. In yet more specific embodiments, the nanostructurescomprise (e.g., on average) at least 95 wt. % metal oxide. In specificembodiments, the nanostructures comprise (e.g., on average) at least 98wt. % metal oxide 1. In more specific embodiments, the nanostructurescomprise (e.g., on average) at least 99 wt. % metal oxide.

In certain embodiments, the nanostructures comprise (e.g., on average)least 50 elemental wt. % metal. In more specific embodiments, metalconstitutes, on average, at least 60 elemental wt. % of thenanostructure(s). In still more specific embodiments, metal constitutes,on average, at least 75 elemental wt. % of the nanostructure(s). In yetmore specific embodiments, metal constitutes, on average, at least 80elemental wt. % of the nanostructure(s). In more specific embodiments,metal constitutes, on average, at least 90 elemental wt. % of thenanostructure(s). In various embodiments, metal constitutes, on average,at least 40 elemental wt. %, at least 70 elemental wt. %, at least 85elemental wt. %, at least 95 elemental wt. %, at least 97 elemental wt.%, at least 98 elemental wt. %, or at least 99 elemental wt. % of thenanostructure(s).

In some embodiments, provided herein are nanostructures comprising anamorphous ceramic and having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 0.2 GPa/nm. In specific instances,provided herein are nanostructures an amorphous ceramic and having amean or median nanofiber Young's modulus-to-diameter ratio of at least0.25 GPa/nm. In more specific instances, provided herein arenanostructures an amorphous ceramic and having a mean or mediannanofiber Young's modulus-to-diameter ratio of at least 0.3 GPa/nm.

In certain embodiments, nanostructures provided herein comprise anamorphous ceramic and have a mean or median nanofiber ultimatestrength-to-bulk ultimate strength of the metal component of at least1:1. In more specific embodiments, nanostructures provided hereincomprise an amorphous ceramic and have a mean or median nanofiberultimate strength-to-bulk ultimate strength of the metal component of atleast 1.2:1.

In certain embodiments, the metal oxide (e.g., ceramic) is in acrystalline state. In specific embodiments, nanostructures providedherein comprise a continuous matrix of crystalline metal oxide (e.g.,ceramic). For example a continuous matrix within a nanostructure iscontinuous along at least 50%, at least 70%, at least 80%, at least 90%,at least 95%, at least 98%, or at least 99% of the length of thenanostructure.

In some embodiments, provided herein are nanostructures comprising acrystalline metal oxide (e.g., ceramic) and having a mean or mediannanofiber Young's modulus-to-diameter ratio of at least 1 GPa/nm. Inspecific instances, provided herein are nanostructures comprising acrystalline ceramic and having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 1.5 GPa/nm. In more specificinstances, provided herein are nanostructures an crystalline metal oxide(e.g., ceramic) and having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 2 GPa/nm.

In certain embodiments, nanostructures provided herein comprise acrystalline metal oxide (e.g., ceramic) and have a mean or mediannanofiber ultimate strength-to-bulk ultimate strength of the metalcomponent of at least 1:1. In more specific embodiments, nanostructuresprovided herein comprise a crystalline metal oxide (e.g., ceramic) andhave a mean or median nanofiber ultimate strength-to-bulk ultimatestrength of the metal component of at least 1.2:1.

In some instances, provided herein are metal oxide (e.g., ceramic)containing nanostructures having a mean or median nanofiber fracturetoughness-to-diameter ratio of at least 0.002 MPa·m^(1/2)/nm. In someinstances, provided herein are nanostructures having a mean or mediannanofiber fracture toughness-to-diameter ratio of at least 0.003MPa·m^(1/2)/nm. In some instances, provided herein are nanostructureshaving a mean or median nanofiber fracture toughness-to-diameter ratioof at least 0.005 MPa·m^(1/2)/nm. In some instances, provided herein arenanostructures having a mean or median nanofiber fracturetoughness-to-diameter ratio of at least 0.007 MPa·m^(1/2)/nm.

Carbides

In some embodiments, nanofibers described herein have improved Young'smodulus over similar materials in other nanostructure or bulk forms. Insome instances, provided herein are nanofibers having a mean or mediannanofiber Young's modulus-to-diameter ratio of at least 0.1 GPa/nm. Incertain instances, provided herein are nanofibers having a mean ormedian nanofiber Young's modulus-to-diameter ratio of at least 0.5GPa/nm. In specific instances, provided herein are nanofibers having amean or median nanofiber Young's modulus-to-diameter ratio of at least 1GPa/nm. In more specific instances, provided herein are nanofibershaving a mean or median nanofiber Young's modulus-to-diameter ratio ofat least 2 GPa/nm. In still more specific instances, provided herein arenanofibers having a mean or median nanofiber Young's modulus-to-diameterratio of at least 3 GPa/nm. In yet more specific instances, providedherein are nanofibers having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 4 GPa/nm. In specific instances,provided herein are nanofibers having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 5 GPa/nm. In some instances,provided herein are nanofibers having a mean or median nanofiber Young'smodulus-to-diameter ratio of at least 0.05 GPa/nm or at least 10 GPa/nm.

In some embodiments, nanofibers described herein have improved fracturetoughness over similar materials in other nanostructure or bulk forms.In some instances, provided herein are nanofibers having a mean ormedian nanofiber fracture toughness-to-diameter ratio of at least 1MPa/nm. In certain instances, provided herein are nanofibers having amean or median nanofiber fracture toughness-to-diameter ratio of atleast 5 MPa/nm. In specific instances, provided herein are nanofibershaving a mean or median nanofiber fracture toughness-to-diameter ratioof at least 10 MPa/nm. In more specific instances, provided herein arenanofibers having a mean or median nanofiber fracturetoughness-to-diameter ratio of at least 15 MPa/nm. In still morespecific instances, provided herein are nanofibers having a mean ormedian nanofiber fracture toughness-to-diameter ratio of at least 20MPa/nm. In yet more specific instances, provided herein are nanofibershaving a mean or median nanofiber fracture toughness-to-diameter ratioof at least 30 MPa/nm. In specific instances, provided herein arenanofibers having a mean or median nanofiber Young's modulus-to-diameterratio of at least 40 MPa/nm. In some instances, provided herein arenanofibers having a mean or median nanofiber Young's modulus-to-diameterratio of at least 0.1 MPa/nm or at least 50 MPa/nm.

In some embodiments, the average electrical conductivity of a nanofiberprovided herein has a log(S/m) to log(S/m) ratio with an identical bulkmaterial of at least 0.3 (i.e., log of the electrical conductivity alongthe length of the nanofiber divided by log of the electricalconductivity of the same material, in bulk—e.g., sheet form). Inspecific embodiments, the average electrical conductivity of a nanofiberprovided herein has a log(S/m) to log(S/m) ratio with an identical bulkmaterial of at least 0.4. In more specific embodiments, the averageelectrical conductivity of a nanofiber provided herein has a log(S/m) tolog(S/m) ratio with an identical bulk material of at least 0.5. In stillmore specific embodiments, the average electrical conductivity of ananofiber provided herein has a log(S/m) to log(S/m) ratio with anidentical bulk material of at least 0.55. In certain embodiments, theaverage electrical conductivity of a nanofiber provided herein is atleast 1 log(S/m), at least 1.5 log(S/m), at least 2 log(S/m), or thelike. In some embodiments, a nanofiber provided herein has aconductivity of at least about 5%, at least about 10%, at least about20%, at least about 30%, at least about 40%, at least about 50%, or thelike when compared with the conductivity of the material when formedinto a sheet. The nanofibers have any suitable electrical conductivity.In various embodiments, electrical conductivity is measured as anaverage value, at a specific condition, or along a specific direction ofthe nanofiber sample. In some embodiments, the conductivity at least 1S/cm, at least 10 S/cm, at least 100 S/cm, at least 10³ S/cm, at least10⁴ S/cm, or the like.

Nanostructure Composite

In certain embodiments, provided herein is a composite comprising aplurality of nanostructures described herein in combination with acomposite matrix material. Depending on the type of properties intendedto impart to the composite, different nanostructures described hereinmay be utilized. By way of non-limiting example, in certain instancesamorphous ceramics are utilized in flexible composites, crystallineceramics are utilized in high strength, low flexibility, and/orinsulating composites, metals are used in conductive composites,carbides are used in for stiff, tough, and/or high strength composites,and the like.

Composites provided herein optionally include any suitable amount of thenanostructures described herein. For example, in certain embodiments,nanostructures or nanostructure compositions (e.g., additivecompositions) provided herein comprise less than 30% by weight of theplurality of nanostructures.

A composite material provided herein may use any suitable matrixmaterial. By way of non-limiting example, the matrix material optionallycomprises a polymer, a metal, a ceramic, a carbide, or the like.

In specific embodiments, the matrix material is a polymer, such as athermoset, thermoplastic, resin, or the like. In more specificembodiments, thermosets include, by way of non-limiting example,unsaturated polyesters, vinyl esters, epoxies, phenolics, polyurethanes,and the like. In certain embodiments, thermoplastics include, by way ofnon-limiting embodiment, polyolefins, such as polyethylene (PE, e.g.,HDPE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (PS),and the like. In certain embodiments, composites are prepared using anysuitable techniques, including, e.g., molding, casting, compounding, orthe like. In some embodiments, the composite matrix material is a metal,such as an elemental metal, such as aluminum or iron, or a metal alloy,such as steel or stainless steel. In certain embodiments, the matrixmaterial is a ceramic, such as silica, zirconia, titania, or the like.In some embodiments, the matrix material is a carbide, such as siliconcarbide. In some embodiments, the composite matrix and thenanostructures (additive) comprise the same material. In otherembodiments, the composite matrix comprises a different material thanthe nanostructures (additive).

Process

Also provided herein are various processes that may be utilized forpreparing the nanostructures described herein. Nanostructures madeaccording to the processes described herein are also considered herein.For example, provided herein are nanostructures produced by treatingprecursor nanofibers that have been electrospun from an aqueous fluidstock, the fluid stock comprising polymer and metal precursor. Inspecific instances, nanostructures described herein are prepared fromelectrospun precursor nanofibers—e.g., following treatment (such asthermal treatment) and/or fracturing of the nanofibers. In someinstances, such nanofibers improved performance characteristics (such asfracture toughness, electrical and thermal conductivity, etc.) comparedto other nanostructure formation techniques, such as those used to makenanowires, including deposition, precipitation, crystal growthtechniques.

In some embodiments, provided herein is a process for producing ananostructure (e.g., for use as a reinforcing additive), the processcomprising:

-   -   a. electrospinning a first fluid stock into an electrospun        material, the first fluid stock comprising (i) a polymer        and (ii) a metal reagent component (e.g., nanoparticles of at        least one metal component, such as a metal oxide, metal        precursor, or a combination thereof);    -   b. treating the electrospun material to provide a nanofiber        nanostructure.

In specific embodiments, the first fluid stock comprises at least onemetal precursor. In more specific embodiments, the first fluid stockcomprises at least one metal precursor and a plurality of nanoparticlescomprising a metal component (e.g., a zero oxidation state metal, ametal oxide, or the like).

In certain embodiments, treatment of the electrospun material comprisesthermal treatment of the electrospun material. In some embodiments,treatment of the electrospun material comprises chemical treatment ofthe electrospun material. In specific embodiments, chemical treatment ofthe electrospun material comprises exposing the electrospun material tooxidative conditions (e.g., air, O₂, peroxide, or the like). In someembodiments, oxidative conditions are utilized to convert the metalprecursor into a metal oxide (e.g., ceramic). In other specificembodiments, chemical treatment of the electrospun material comprisesexposing the electrospun material to reducing conditions (e.g., H₂, orthe like). In certain embodiments, treatment of the electrospun materialcomprises both thermal and chemical treatment. In some embodiments,treatment of the electrospun material is performed under an inertatmosphere (e.g., N₂, Ar, or the like).

In some embodiments, thermal treatment (e.g., calcination) is performedat about 100° C., about 150° C., about 200° C., about 300° C., about400° C., about 500° C., about 600° C., about 700° C., about 800° C.,about 900° C., about 1,000° C., about 1,500° C., about 2,000° C., andthe like. In some embodiments, calcination is performed at a temperatureof at least 100° C., at least 150° C., at least 200° C., at least 300°C., at least 400° C., at least 500° C., at least 600° C., at least 700°C., at least 800° C., at least 900° C., at least 1,000° C., at least1,500° C., at least 2,000° C., and the like. In some embodiments,thermal treatment (e.g., calcination) is performed at a temperature ofat most 100° C., at most 150° C., at most 200° C., at most 300° C., atmost 400° C., at most 500° C., at most 600° C., at most 700° C., at most800° C., at most 900° C., at most 1,000° C., at most 1,500° C., at most2,000° C., and the like. In some embodiments, thermal treatment (e.g.,calcination) is performed at a temperature of between about 300° C. and800° C., between about 400° C. and 700° C., between about 500° C. and900° C., between about 700° C. and 900° C., between about 800° C. and1,200° C., and the like. In some embodiments, thermal treatment (e.g.,calcination) is performed at a constant temperature. In someembodiments, the temperature changes over time. Thermal treatment (e.g.,calcination) is performed for any suitable amount of time (e.g., asnecessary to arrive at a nanofiber nanostructure with the desiredproperties). In some instances, treatment (e.g., thermal treatment) ofthe electrospun nanofiber allows the carbonaceous and organic materialto be removed from the resultant treated nanofiber nanostructure. Inother instances, treatment (e.g., thermal treatment) of the electrospunnanofiber allows the carbonaceous material (polymer) in proximity to theprecursor to react with the precursor, resulting in a metal carbide. Insome instances, formation of a carbide is achieved by thermal treatmentat a temperature above the temperature required to simplydegrade/decompose and remove the organic material (e.g., at atemperature of about 1,000° C. to about 1,700° C.). In more specificembodiments, carbonization of the polymer and reaction of the carbonizedpolymer with the metal reagent component comprises heating the nanofiberat a temperature suitable to carbonize the polymer and cause thecarbonized polymer to react with the metal component. In certainembodiments, the nanofiber is heated to a temperature of about 900° C.to about 2000° C., at least 900° C., at least 1000° C., or the like. Inspecific embodiments, the nanofiber is heated to a temperature of about1000° C. to about 1800° C., or about 1000° C. to about 1700° C. In someinstances, thermal treatment is performed at a suitable temperature toconvert the metal reagent component (e.g., metal precursor) into themetal component and at least partially convert the organic material(e.g., polymer) into a carbon matrix (e.g., an amorphous continuouscarbon matrix) (e.g., at a temperature of about 400° C. to about 1400°C. under inert conditions). In more specific embodiments, carbonizationof the polymer to a continuous carbon matrix comprises heating thenanofiber at a temperature suitable to carbonize the polymer, but nothigh enough to remove the polymer and/or cause the carbonized polymer toreact with the metal or metal reagent component. In certain embodiments,the nanofiber is heated to a temperature of about 400 to about 1400° C.In specific embodiments, the nanofiber is heated to a temperature ofabout 400° C. to about 1200° C., or about 600° C. to about 1200° C.

In some embodiments, treatment is performed at a constant or variabletemperature. In some embodiments, the treatment conditions compriseusing a temperature gradient. In some embodiments, the temperatureincreases from a first temperature (e.g., the temperature of theelectrospinning process, optionally room temperature) to a secondtemperature. In certain embodiments, treatment conditions compriseutilization of a temperature increase during the treatment process. Insome instances, the rate of temperature increase is any suitable rate,for example about 1° C./min to about 35° C./min. In some embodiments,the treatment occurs for any suitable amount of time. In specificembodiments, the dwell time at the maximum (second) temperature occursfor 10 minutes to 20 hours, or any other suitable amount of time.

In some embodiments, treatment procedures are performed under inertconditions (e.g., under argon or nitrogen). In some instances, treatmentprocedures are performed under reducing conditions (e.g., underhydrogen, or a mixture of hydrogen and argon). In some embodiments, if ametal component that is a metal is desired, treatment procedures areperformed under such reducing or inert conditions. In furtherembodiments, treatment procedures are performed under oxidativeconditions (e.g., under air or other oxygen containing gases). In someembodiments, if a metal component that is a metal oxide or ceramic isdesired, treatment procedures are performed under oxidative conditions.In some embodiments, treatment conditions include gaseous conditions,liquid conditions, or the like.

In some instances, a process described herein further compriseselectrospinning a second fluid about a common axis with the first fluidstock, whereby electrospinning the first and second fluid togetherprovide the electrospun material. In some instances, common-axial(co-axial) electrospinning of a first and second fluid stock provide alayered hybrid structure, such as one described herein. In some of suchinstances, the second fluid stock comprises a metal precursor and apolymer in an aqueous medium. In some embodiments, treatment (e.g.,thermal and/or chemical treatment) of the precursor material or layerelectrospun from the second fluid stock serves to convert the metalprecursor into a metal component described herein. Alternatively, thesecond fluid is a gas, which assists production and drying of anelectrospun nanofiber comprising precursor material. Hollow nanofibersare optionally produced by using a second fluid that is a gas and thatis electrospun about a common axis with the first fluid and the firstfluid is outside the second fluid (i.e., the first fluid is further fromthe common axis than the second fluid).

In some embodiments, a process provided herein further comprisesfunctionalizing the surface of the electrospun material or of thetreated material. In some instances, such functionalization is achievedthrough further thermal treatment and/or chemical treatment.

In certain embodiments, a process provided herein further comprisesfracturing the electrospun or treated material. In some instances,fracturing of the treated, electrospun material provides a tunableprocess for preparing nanostructures with a desired aspect ratio and/orlength. In various embodiments, fracturing of the electrospun or treatedmaterial is achieved via any suitable process. In specific embodiments,such processes include, by way of non-limiting example, steps ofsonicating, pressuring, grinding, chemical etching, laser irradiation,or any combination thereof the electrospun or treated material.

In one aspect, the process has a high yield (e.g., which is desirablefor embodiments in which the precursor is expensive). In someembodiments, the metal atoms in the nanostructure(s) are about 10%,about 20%, about 30%, about 33%, about 40%, about 50%, about 60%, about70%, about 80%, about 90%, about 95%, about 98%, or about 100% of thenumber of (e.g., in moles) metal molecules in the fluid stock (i.e.,present in the metal reagent components thereof). In some embodiments,the metal atoms in the nanostructures are at least 10%, at least 20%, atleast 30%, at least 33%, at least 40%, at least 50%, at least 60%, atleast 70%, at least 80%, at least 90%, at least 95%, at least 98%, or atleast 99% of the moles of metal molecules in the fluid stock. In someembodiment, the moles of precursor molecules in the nanostructure arebetween about 10% and about 40%, between about 20% and about 50%, orbetween about 50% and about 100% of the moles of metal molecules in thefluid stock.

FIG. 1 illustrates an exemplary schematic of a process described herein.In some instances, a first composition comprising metal reagentcomponent 101 (e.g., metal precursor, such as an acetate of Ag, Al, Co,Fe, Ni, Zn, Zr, Si, etc.) is combined 102 with a second compositioncomprising a polymer 103 (e.g., PVA, PVAc, PVEO, etc.) to prepare afluid stock 104 (e.g., comprising a metal reagent component andpolymer—unassociated, partially associated, or completely associatedwith metal reagent component). In some instances, a fluid stock providedherein is electrospun using an electrospinning apparatus, such as asyringe system 105, through a nozzle 106, wherein the nozzle isoptionally heated and may optionally comprise a coaxially aligned gasnozzle for expressing gas along the same longitudinal axis as the fluidstock jet (i.e., the precursor nanofiber). In certain embodiments,electrospinning of the fluid stock produces a precursor nanofiber 108,comprising metal precursor and polymer (e.g., in a weight ratio of over1:2 and up to 4:1), the precursor nanofiber being collected on acollector 107. Treatment 109 (e.g., thermal and/or chemical treatment,producing nanofiber nanostructures, followed by optional fragmentationof the nanofiber nanostructures) of the precursor nanofiber 108 may thenbe performed (e.g., with a heater and/or in a reaction vessel/chamber)to produce nanostructure product 110.

FIG. 2 illustrates an exemplary schematic of a process or apparatusdescribed herein, particularly for preparing a layered nanocompositenanostructures by a coaxial gas assisted electrospinning process. Insome instances, a first fluid stock 201 (e.g., comprising a metalreagent component and a polymer), is electrospun with an optional secondfluid stock 202 (e.g., comprising a second metal precursor and a secondpolymer, the second precursor and polymer independently being either thesame or different from the first), and a third fluid (e.g., gas) 203.The fluid stocks may be provided to the apparatus by any device, e.g.,by a syringe 205. And the gas may be provided from any source 206 (e.g.,air pump). In some embodiments such an apparatus comprises a pluralityof co-axial needles 204. Exemplary needles, as illustrates by the crosssection 207, comprise an outer sheath tube 208 (e.g., having a supplyend and a nozzle end), at least one intermediate tube 209 (e.g., havinga supply end and a nozzle end), and a core tube 210 (e.g., having asupply end and a nozzle end). In specific instances, each of the tubesare coaxially aligned (i.e., aligned along the substantially same axis).In certain embodiments, such a process may be utilized to prepare ananofiber comprising a core and a layer. In some embodiments, theintermediate tube may be absent and a fluid stock may be electrospun ina gas-assisted manner (i.e., the sheath tube provides a high velocitygas). In other embodiments, the fluid stock may be electrospun from thesheath tube, the intermediate tube may be absent and the gas may beprovided from the core tube (e.g., to produce a hollow nanofiber, whichmay be further treated/processed according to the techniques describedherein to produce a hollow nanostructure). In some instances, the tubeor nozzle end of any tube (e.g., any tube providing a fluid stock is)heated or capable of being heated. In some instances, heating of thenozzle provides for improved electrospinning performance and/orelectrospun nanofiber morphology.

Fluid Stock Components

In certain embodiments, the first fluid stock comprises at least onepolymer and at least one metal reagent component (e.g., metalprecursor). In specific embodiments, the first fluid stock comprises anaqueous medium. In some embodiments, the fluid stock comprises at leastone metal precursor in association with one or more of the at least onepolymer.

In some embodiments, high loading of metal reagent component (e.g.,concentration and/or relative to polymer) and homogeneity in fluidstocks and/or precursor nanofibers facilitate and/or provide pure and/oruniform nanostructures following treatment. In certain instances, fewdefects and/or voids are created in the nanofiber when upon treatmentcompared to the number of defects and/or voids created when having lowerprecursor loading.

In various embodiments, the fluid stock comprises a substantiallyuniform and/or homogenous dispersion or solution (e.g., as measured byviscosity deviations, UV absorbance, or the like). In some embodiments,the fluid stock is aqueous (i.e., comprises water). In certaininstances, use of water in the fluid stock facilitates the dispersion ofthe metal reagent component (e.g., metal precursor), facilitates formingmetal reagent component-polymer associations in the fluid stock, andfacilitates forming a uniform and/or homogenous dispersion/solution.

In some embodiments, the fluid stock uniform or homogenous. In specificembodiments, the process described herein comprises maintaining fluidstock uniformity or homogeneity. In some embodiments, fluid stockuniformity and/or homogeneity is achieved or maintained by any suitablemechanism, e.g., by agitating, heating, or the like. Methods ofagitating include, by way of non-limiting example, mixing, stirring,shaking, sonicating, or otherwise inputting energy to prevent or delaythe formation of more than one phase in the fluid stock. In someembodiments, the fluid stock is continually agitated. In someembodiments, the fluid stock is agitated to create a uniform dispersionor solution, which is then used in an electrospinning step before thefluid stock (e.g., dispersion or solution) loses uniformity and/orhomogeneity (e.g., it before it separates into more than one phase).

In some embodiments, a fluid stock is prepared by (i) dissolving ordispersing a metal reagent (e.g., precursor) in a first fluid (e.g.,water, or another aqueous medium) to form a first composition; (ii)dissolving or dispersing a polymer in a second fluid (e.g., water, oranother aqueous medium) to form a second composition; and (iii)combining at least a portion of the first and second compositions toform the fluid stock.

In some embodiments, a fluid stock provided herein is prepared bycombining a metal reagent component and a polymer in an aqueous medium(e.g., in water). In some embodiments, a metal reagent component iscombined with the polymer in a metal reagent component to polymerweight-to-weight ratio of at least 1:2 (e.g., at least 1:1). In certainembodiments, a first metal reagent component is combined with a polymer,forming an association (e.g., via a ligand replacement reaction) betweenthe polymer and a second metal reagent component (e.g., a metal-ligandcomplex wherein one of the ligands of the first metal reagent componentis replaced with a polymer moiety). In some embodiments, a fluid stockprovided herein may comprise both first and second metal reagentcomponents (e.g., polymer-associated and non-associated metal reagentcomponents). For the purposes of concentration and embodiments herein,reference to a metal reagent component encompasses any metal reagentcomponent present in the fluid stock, whether it is associated with thepolymer or not. Similarly, polymer concentration and embodimentsprovided herein encompass polymer in associated and non-associatedforms. Reference to the polymer refers only to the polymer moiety ofsuch an association, and reference to the precursor refers to theprecursor moiety of such an association. FIG. 3 illustrates an exemplarymetal reagent precursor 301 combined with a polymer 302 to provide ametal precursor-polymer association 303. In some instances such anassociation process may be complete (i.e., all metal reagent precursorand/or polymer reactive sites may be associated), and in otherinstances, some of the metal reagent precursor and/or polymer reactivesites (e.g., —OH groups for the PVA of FIG. 3) may remain unassociated.In other words, in some instances, x hydroxyl groups of the PVA may beassociated with the precursor, and n-x hydroxyl groups may remainunassociated. Such associations may be monitored in any suitable manner,e.g., by infrared (IR) spectrometry, nuclear magnetic resonance (NMR)spectrometry, mass spectrometry (MS, e.g., GCMS), or the like.

In some aspects, the polymer is soluble in water, meaning that it formsa solution in water. In other embodiments, the polymer is swellable inwater, meaning that upon addition of water to the polymer the polymerincreases its volume up to a limit. Water soluble or swellable polymersare generally at least somewhat hydrophilic. In some embodiments, apolymer described herein is a polymer that is electrophilic ornucleophilic. In some instances, a nucleophilic or electrophilic polymeris matched with a complementary precursor (e.g., a nucleophilic polymer,such as PVA, is matched with a electrophilic precursor, such as a metalacetate). Exemplary polymers suitable for the present methods includebut are not limited to polyvinyl alcohol (“PVA”), polyvinyl acetate(“PVAc”), polyethylene oxide (“PEO”), polyvinyl ether, polyvinylpyrrolidone, polyglycolic acid, hydroxyethylcellulose (“HEC”),ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate, andthe like. In some embodiments, the polymer is isolated from biologicalmaterial. In some embodiments, the polymer is starch, chitosan, xanthan,agar, guar gum, and the like.

In some embodiments, a polymer described herein (e.g., in a process,precursor nanofiber, a fluid stock, or the like) is a polymer (e.g.,homopolymer or copolymer) comprising a plurality of reactive sites. Incertain embodiments, the reactive sites are nucleophilic (i.e., anucleophilic polymer) or electrophilic (i.e., an electrophilic polymer).For example, in some embodiments, a nucleophilic polymer describedherein comprises a plurality of alcohol groups (such as polyvinylalcohol—PVA—or a cellulose), ether groups (such as polyethyleneoxide—PEO—or polyvinyl ether—PVE), and/or amine groups (such aspolyvinyl pyridine, ((di/mono)alkylamino)alkyl alkacrylate, or thelike).

In certain embodiments, the polymer is a nucleophilic polymer (e.g., apolymer comprising alcohol groups, such as PVA). In some embodiments,the polymer is a nucleophilic polymer and a first precursor (e.g.,reagent precursor) is an electrophilic precursor (e.g., a metal acetate,metal chloride, or the like). In specific embodiments, theprecursor-polymer association is a reaction product between anucleophilic polymer and an electrophilic first precursor (e.g., reagentprecursor).

In other embodiments, the polymer is an electrophilic polymer (e.g., apolymer comprising chloride or bromide groups, such as polyvinylchloride). In some embodiments, the polymer is an electrophilic polymerand a first precursor (e.g., reagent precursor) is a nucleophilicprecursor (e.g., metal-ligand complex comprising “ligands” withnucleophilic groups, such as alcohols or amines). In specificembodiments, the precursor-polymer association is a reaction productbetween an electrophilic polymer and a nucleophilic first precursor.

In some embodiments, the polymer imparts a suitable elongationalviscosity to the fluid stock for electrospinning nanofibers. In someembodiments, low shear viscosity leads to beaded nanofibers. In oneaspect, uniform distribution of the precursor in the fluid feed helps tomaintain a suitably high elongational viscosity.

Generally, a fluid stock provided herein has a fluidity and viscositysuitable for electrospinning. In some embodiments, a fluid stockprovided herein is a solution, a dispersion, or the like. In specificembodiments, a or all fluid stocks used in a process herein are aqueousfluid stocks (with optional gas fluid(s) also electrospun about a commonaxis). Viscosity is a measure of the resistance of a fluid which isbeing deformed by either shear stress or tensile stress. Viscosity ismeasured in units of poise. In various embodiments, the viscosity of thepolymer or fluid stock is measured with or without associated precursor.The polymer or fluid stock has any suitable elongational viscosity. Insome embodiments, the polymer or fluid stock has an elongationalviscosity of about 50 poise, about 100 poise, about 200 poise, about 300poise, about 400 poise, about 500 poise, about 600 poise, about 800poise, about 1000 poise, about 1500 poise, about 2000 poise, about 2500poise, about 3000 poise, about 5,000 poise, and the like. In someembodiments, the polymer or fluid stock has an elongational viscosity ofat least 50 poise, at least 100 poise, at least 200 poise, at least 300poise, at least 400 poise, at least 500 poise, at least 600 poise, atleast 800 poise, at least 1,000 poise, at least 1,500 poise, at least2,000 poise, at least 2,500 poise, at least 3,000 poise, at least 5,000poise, and the like. In some embodiments, the polymer or fluid stock hasan elongational viscosity of at most 50 poise, at most 100 poise, atmost 200 poise, at most 300 poise, at most 400 poise, at most 500 poise,at most 600 poise, at most 800 poise, at most 1,000 poise, at most 1,500poise, at most 2,000 poise, at most 2,500 poise, at most 3,000 poise, atmost 5,000 poise, and the like. In some embodiments, the polymer orfluid stock has an elongational viscosity of between about 100 and 3,000poise, or between about 1,000 and 5,000 poise, and the like.

Molecular weight is related to the mass of the monomers comprising thepolymer and the degree of polymerization. In some embodiments, molecularweight is a factor that affects viscosity. The polymer has any suitablemolecular weight. In some embodiments, the polymer has a molecularweight of at least 20,000 atomic mass units (“amu”), at least 50,000amu, at least 100,000 amu, at least 200,000 amu, at least 300,000 amu,at least 400,000 amu, at least 500,000 amu, at least 700,000 amu, or atleast 1,000,000 amu and the like. In some embodiments, the polymer has amolecular weight of at most 20,000 amu, at most 50,000 amu, at most100,000 amu, at most 200,000 amu, at most 300,000 amu, at most 400,000amu, at most 500,000 amu, at most 700,000 amu, or at most 1,000,000 amuand the like. In some embodiments, the polymer has a molecular weight ofabout 20,000 amu, about 50,000 amu, about 100,000 amu, about 200,000amu, about 300,000 amu, about 400,000 amu, about 500,000 amu, about700,000 amu, or about 1,000,000 amu and the like. In yet otherembodiments, the polymer has a molecular weight of from about 50,000 amuto about 1,00,000 amu, from about 100,000 amu to about 500,000 amu, fromabout 200,000 amu to about 400,000 amu, or from about 500,000 amu toabout 1,00,000 amu and the like.

The polydispersity index (“PDI”) is a measure of the distribution ofmolecular mass in a given polymer sample. The PDI is the weight averagemolecular weight divided by the number average molecular weight, whichis calculated by formula known to those skilled in the art of polymerscience. The polymer has any suitable polydispersity index. In someembodiments, the polymer has a polydispersity index of about 1, about 2,about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10,about 15, about 20, and the like. In some embodiments, the polymer has apolydispersity index of at least 1, at least 2, at least 3, at least 4,at least 5, at least 6, at least 7, at least 8, at least 9, at least 10,at least 15, at least 20, and the like. In some embodiments, the polymerhas a polydispersity index of at most 1, at most 2, at most 3, at most4, at most 5, at most 6, at most 7, at most 8, at most 9, at most 10, atmost 15, at most 20, and the like. In some embodiments, the polymer hasa polydispersity index of about 1 to about 10, about 2 to about 5, andthe like.

In some examples, high loading of precursor on the polymer in the fluidstock is beneficial for obtaining pure and/or uniform nanofibers. Asdescribed herein, few defects and/or voids are created in the nanofiberwhen the polymer is removed compared to the number of defects and/orvoids created when having lower precursor loading. In some instances,loading is represented as the weight ratio of the metal reagentcomponent to polymer in the fluid stock or precursor nanofiber (themetal reagent component being in associated and/or non-associated form).The weight ratio of the metal reagent component to polymer is any valueresulting in a nanofiber with suitable properties in a given embodiment.The weight ratio of the metal reagent component to polymer is at least1:2 in some embodiments. In other embodiments, the ratio is at least1:9, at least 1:8, at least 1:7, at least 1:6, at least 1:5, at least1:4, at least 1:3, at least 1:2, at least 1:1.75, at least 1:1.5, or atleast 1:1.25. In other embodiments there is about equal weights of metalreagent component and polymer. In some embodiments, there is more metalreagent component than polymer by weight. In some embodiments, theweight ratio of the metal reagent component to polymer is at least1.25:1, at least 1.5:1, at least 1.75:1, at least 2:1, at least 3:1, orat least 4:1. In yet other embodiments, the weight ratio of metalreagent component to polymer is about 1:2 to about 5:1, or about 1:1 toabout 4:1. In some embodiments, all or part of the metal reagentcomponent is associated with the polymer and the metal reagent componentto polymer weight-to-weight ratio is determined by the ratio of the sumof the associated and non-associated metal reagent component to thepolymer.

The fluid stock contains any suitable amount of polymer. The weightpercent of polymer in the fluid stock is represented as the weightpercent of polymer (whether the polymer is associated with metal reagentor not). In some embodiments, the fluid stock comprises at least about0.5 weight %, at least about 1 weight %, at least about 2 weight %, atleast about 3 weight %, at least about 4 weight %, at least about 5weight %, at least about 6 weight %, at least about 7 weight %, at leastabout 8 weight %, at least about 9 weight %, at least about 10 weight %,at least about 12 weight %, at least about 14 weight %, at least about16 weight %, at least about 18 weight %, at least about 20 weight %, atleast about 30 weight %, or at least about 40 weight % polymer. In someembodiments, the fluid stock comprises from about 1 weight % to about 20weight % polymer. In some embodiments, the fluid stock comprises fromabout 1 weight % to about 10 weight %, from about 1 weight % to about 5weight %, from about 5 weight % to about 20 weight %, from about 5weight % to about 10 weight %, from about 10 weight % to about 15 weight%, or from about 15 weight % to about 20 weight % polymer.

In certain embodiments, polymer concentration in the fluid stock isdetermined on a monomeric residue concentration. In other words, theconcentration of the polymer is determined based on the concentration ofpolymeric repeat units present in the stock. For example, polymerconcentration of polyvinyl alcohol may be measured based on theconcentration of (—CH₂CHOH—) present in the fluid stock. In someembodiments, the monomeric residue (i.e., repeat unit) concentration ofthe polymer in the fluid stock is at least 100 mM. In specificembodiments, the monomeric residue (i.e., repeat unit) concentration ofthe polymer in the fluid stock is at least 200 mM. In more specificembodiments, the monomeric residue (i.e., repeat unit) concentration ofthe polymer in the fluid stock is at least 400 mM. In still morespecific embodiments, the monomeric residue (i.e., repeat unit)concentration of the polymer in the fluid stock is at least 500 mM. Inat least 5 mM, at least 100 mM, at least 150 mM, at least 200 mM, atleast 250 mM, at least 300 mM, at least 350 mM, at least 400 mM, atleast 500 mM, at least 700 mM, at least 900 mM, at least 1.2 M, at least1.5 M, at least 2 M, at least 5 M, and the like. In some embodiments,the concentration of the monomeric residue in the fluid stock is between5 mM and 5 M, between 200 mM and 1 M, between 100 mM and 700 mM, and thelike. In some embodiments, the concentration of metal reagent (e.g.,precursor) in the fluid stock to monomeric residue in the fluid stock isat least 1:4. In specific embodiments, the concentration of metalreagent (e.g., precursor) in the fluid stock to monomeric residue in thefluid stock is at least 1:3. In more specific embodiments, theconcentration of metal reagent (e.g., precursor) in the fluid stock tomonomeric residue in the fluid stock is at least 1:2. In still morespecific embodiments, the concentration of metal reagent (e.g.,precursor) in the fluid stock to monomeric residue in the fluid stock isat least 1:1.2. In yet more specific embodiments, the concentration ofmetal reagent (e.g., precursor) in the fluid stock to monomeric residuein the fluid stock is about 1:1 (e.g., within 5%). In other embodiments,the concentration of metal reagent (e.g., precursor) in the fluid stockto monomeric residue in the fluid stock is at least 1:10, at least 1:8,at least 1:6, at least 1:1.5, at least 1:3.5, at least 1:2.5, or anysuitable ratio.

In some embodiments, the fluid stock comprises metal reagent (e.g.,precursor) and polymer, wherein at least 5 elemental wt. % of the totalmass of the metal reagent (e.g., precursor) and polymer is metal. Incertain embodiments, at least 10 elemental wt. % of the total mass ofthe metal reagent (e.g., precursor) and polymer is metal. In specificembodiments, at least 15 elemental wt. % of the total mass of the metalreagent (e.g., precursor) and polymer is metal. In more specificembodiments, at least 20 elemental wt. % of the total mass of the metalreagent (e.g., precursor) and polymer is metal. In specific embodiments,at least 25 elemental wt. % of the total mass of the metal reagent(e.g., precursor) and polymer is metal. In still more specificembodiments, at least 30 elemental wt. % of the total mass of the metalreagent (e.g., precursor) and polymer is metal. In yet more specificembodiments, at least 35 elemental wt. % of the total mass of the metalreagent (e.g., precursor) and polymer is metal. In more specificembodiments, at least 40 elemental wt. % of the total mass of the metalreagent (e.g., precursor) and polymer is metal. In various embodiments,at least 10 elemental wt. %, at least 15 elemental wt. %, at least 45elemental wt. %, at least 50 elemental wt. % of the total mass of themetal reagent (e.g., precursor) and polymer is metal.

In one aspect, the concentration of metal reagent (e.g., precursor) inthe fluid stock is high. The concentration is any suitableconcentration. In some embodiments, the concentration of the metalreagent (e.g., precursor) in the fluid stock is about 5 mM, about 10 mM,about 20 mM, about 40 mM, about 60 mM, about 80 mM, about 100 mM, about150 mM, about 200 mM, about 250 mM, about 300 mM, about 350 mM, about400 mM, about 500 mM, about 700 mM, about 900 mM, about 1.2 M, about 1.5M, about 2 M, about 5 M, and the like. In some embodiments, theconcentration of the metal reagent (e.g., precursor) in the fluid stockis at least 5 mM, at least 10 mM, a at least 20 mM, at least 40 mM, atleast 60 mM, at least 80 mM, at least 100 mM, at least 150 mM, at least200 mM, at least 250 mM, at least 300 mM, at least 350 mM, at least 400mM, at least 500 mM, at least 700 mM, at least 900 mM, at least 1.2 M,at least 1.5 M, at least 2 M, at least 5 M, and the like. In someembodiments, the concentration of the metal reagent (e.g., precursor) inthe fluid stock is between 5 mM and 5 mM, between 20 mM and 1 M, between100 mM and 700 mM, between 100 mM and 300 mM, and the like.

In some embodiments, the fluid stock and/or precursor nanofibercomprises a high loading of metal reagent component. In someembodiments, the polymer is at least 20% loaded with metal reagentcomponent (i.e., at least 20% of the reactive sites of the polymer areassociated with a metal reagent component). In specific embodiments, thepolymer is at least 35% loaded with metal reagent component. In morespecific embodiments, the polymer is at least 50% loaded with metalreagent component. In still more specific embodiments, the polymer is atleast 75% loaded with metal reagent component. In various embodiments,the polymer is at least 20%, at least at least 30%, at least 40%, atleast 50%, at least 60%, at least 70%, at least 75%, at least 80%, atleast 85%, at least 85%, at least 90%, at least 95%, at least 96%, atleast 97%, at least 98%, or at least 99% loaded with metal reagentcomponent. In some instances, the polymer is about 50% to 100%, about70% to 100%, about 90% to 100%, about 50% to about 90%, about 60% toabout 80%, or about 20% to about 50% loaded with metal reagentcomponent. In some embodiments, the metal reagent component present inthe fluid stock or precursor nanofiber is at least 80% associated withthe polymer. In more specific embodiments, the precursor present in thefluid stock is at least 90% associated with the polymer. In still morespecific embodiments, the precursor present in the fluid stock is atleast 95% associated with the polymer. In other specific embodiments,the precursor present in the fluid stock is at least 20%, at least 30%,at least 40%, at least 50%, at least 60%, at least 70%, at least 75%, atleast 85%, at least 98%, or at least 99% associated with the polymer.Loading and/or association between metal reagent component and polymercan be determined by any suitable mechanism, e.g., nuclear magneticresonance (NMR) spectrometry, infrared (IR) spectrometry, or the like.For example, FIG. 4 illustrates the increased loading of precursor onthe polymer (e.g., by the decreasing intensity of the —OH peak).

Any suitable precursor is optionally utilized in any processes describedherein. In some embodiments, the precursor is a metal-ligand (e.g.,complex, salt, or the like). In some embodiments, precursors includemetal associations with acetate, iodide, bromide, sulfide, thiocyanate,chloride, nitrate, azide, fluoride, hydroxide, oxalate, water, nitrite,isothiocyanate, acetonitrile, pyridine, ammonia, ethylenediamine,2,2′-bipyridine, 1,10-phenanthroline, nitrite, triphenylphosphate,cyanide, carbon monoxide, or alkyl-oxide. In specific examples, theprecursor is a metal-ligand such as metal acetate (e.g., Al(OCOCH₃)₃),metal chloride, metal nitrate, or metal alkyl-oxide. In specificembodiments, the metal precursor is a metal-ligand association (complex)(e.g., a coordination complex), each metal precursor comprising metalatom(s) associated (complexed) with one or more ligand(s) (e.g., 1-10,2-9, or any suitable number of ligands). In specific embodiments, theprecursor described herein comprises at least two different types ofligand (e.g., at least one acetate and at least one halide). In someembodiments, the precursor is a metal carboxylate (e.g., —OCOCH₃ oranother —OCOR group, wherein R is an alkyl, substituted alkyl, aryl,substituted aryl, or the like). In certain embodiments, the precursor isa metal nitrate. In some embodiments, the precursor is a metal alkoxide(e.g., a methoxide, ethoxide, isopropyl oxide, t-butyl oxide, or thelike). In some embodiments, the precursor is a metal halide (e.g.,chloride, bromide, or the like). In certain embodiments, the precursoris a diketone (e.g., acetylacetone, hexafluoroacetylacetone, or thelike). In other embodiments, any suitable ligand may be utilized in ametal-ligand association (metal precursor) described herein, e.g.,ketones, diketones (e.g., a 1,3-diketone, such as ROCCHR′COR group,wherein R is an alkyl, substituted alkyl, aryl, substituted aryl and R′is R or H), carboxylates (e.g., acetate or —OCOR group, wherein each Ris independently an alkyl, substituted alkyl, aryl, substituted aryl),halides, nitrates, amines (e.g., NR′₃, wherein each R″ is independentlyR or H or two R″, taken together form a heterocycle or heteroaryl), andcombinations thereof. Further examples include iodide, bromide, sulfide(e.g., —SR), thiocyanate, chloride, nitrate, azide, fluoride, hydroxide,oxalate, water, nitrite (e.g., RN₃), isothiocyanate, acetonitrile,pyridine, ammonia, ethylenediamine, 2,2′-bipyridine,1,10-phenanthroline, nitrite, triphenylphosphate, cyanide, carbonmonoxide, or alko-oxide. Metals for such metal reagent components (e.g.,metal precursors) are any suitable metal, including those as describedherein for the metal component.

In some instances, there is some cross-linking between polymers, e.g.,through a metal reagent component. In some embodiments, the polymers ofa fluid stock described herein are less than 20% cross-linked (e.g.,less than 20% of the metal reagent component are associated with 2 ormore polymers and/or less than 20% of the monomeric units of the polymerare connected, e.g., via a metal reagent component, to another polymer).In some embodiments, the polymers are less than 10% cross-linked. Inspecific embodiments, the polymers are less than 5% cross-linked. Inmore specific embodiments, the polymers are less than 3% cross-linked.In still more specific embodiments, the polymers are less than 2%cross-linked. In yet more specific embodiments, the polymers are lessthan 1% cross-linked.

In some embodiments, precursor nanofibers provided herein comprise apolymer and (e.g., on average) at least 5 elemental wt. % metal. Incertain embodiments, precursor nanofibers provided herein comprise apolymer and (e.g., on average) at least 10 elemental wt. % metal. Inspecific embodiments, precursor nanofibers provided herein comprise apolymer and (e.g., on average) at least 15 elemental wt. % metal. Inmore specific embodiments, precursor nanofibers provided herein comprisea polymer and (e.g., on average) at least 20 elemental wt. % metal. Inspecific embodiments, metal constitutes (e.g., on average) at least 25elemental wt. % precursor nanofiber(s). In still more specificembodiments, metal constitutes (e.g., on average) at least 30 elementalwt. % of the precursor nanofiber(s). In yet more specific embodiments,metal constitutes (e.g., on average) at least 35 elemental wt. % of theprecursor nanofiber(s). In more specific embodiments, metal constitutes(e.g., on average) at least 40 elemental wt. % of the precursornanofiber(s). In various embodiments, metal constitutes (e.g., onaverage) at least 10 elemental wt. %, at least 15 elemental wt. %, atleast 45 elemental wt. %, at least 50 elemental wt. % of the precursornanofiber(s).

In some embodiments, an electrospun precursor nanofiber comprises metalreagent component and polymer, wherein the metal reagent component andpolymer when taken together make up at least 50%, at least 60%, at least70%, at least 80%, at least 90%, at least 95%, or at least 98% of thetotal mass of the nanofiber.

In some instances, a process of preparing nanostructures may leavedefects such as gaps, voids, and the like in the resultant nanofiber. Insome embodiments, these defects are reduced by increasing the proportionof metal reagent component in the fluid stock and/orprecursor/electrospun nanofiber relative to the amount of polymer. Insome embodiments, increasing homogeneity of the fluid stock reduces thevoids and/or defects in the nanofiber compared to when the fluid stockis not homogenous. In some instances, when the fluid feed is electrospunand converted to a nanofiber, use of homogenous fluid feed leads to ahomogenous electro spun nanofiber.

In some embodiments, associating the precursor with the polymer, such asthrough a chemical bond between the precursor and polymer results inlong, high quality nanofibers with few defects compared to embodimentswithout an association between the precursor and polymer. In someinstances, the precursor is distributed relatively homogenously on thepolymer (e.g., such that electrospinning of the fluid stock having suchhomogenous associations provides nanofibers with few voids and defects).In addition to the association, it is advantageous in some embodimentsto first create a homogenous solution of precursor before combining theprecursor and polymer.

Electrospinning

In some embodiments, the process comprises electrospinning a fluidstock. Any suitable method for electrospinning is used. In someinstances, elevated temperature electrospinning is utilized. Exemplarymethods for comprise methods for electrospinning at elevatedtemperatures as disclosed in U.S. Pat. No. 7,326,043 and U.S. Pat. No.7,901,610, which are incorporated herein for such disclosure. In someembodiments, elevated temperature electrospinning improves thehomogeneity of the fluid stock throughout the electrospinning process.In some embodiments, gas assisted electrospinning is utilized (e.g.,about a common axis with the jet electrospun from a fluid stockdescribed herein). Exemplary methods of gas-assisted electrospinning aredescribed in PCT Patent Application PCT/US2011/024894 (“Electrospinningapparatus and nanofibers produced therefrom”), which is incorporatedherein for such disclosure. In gas-assisted embodiments, the gas isoptionally air or any other suitable gas (such as an inert gas,oxidizing gas, or reducing gas). In some embodiments, gas assistanceincreases the throughput of the process and/or reduces the diameter ofthe nanofibers. In some instances, gas assisted electrospinningaccelerates and elongates the jet of fluid stock emanating from theelectrospinner. In some embodiments, incorporating a gas stream inside afluid stock produces hollow nanofibers. In some embodiments, the fluidstock is electrospun using any method known to those skilled in the art.

In some embodiments, electrospinning is achieved by electrospinning afluid stock through a nozzle apparatus, the nozzle apparatus having aninner needle and an outer needle (e.g., wherein the inner and outerneedles are arranged concentrically or along a common axis). In someembodiments, the fluid stock is electrospun through the inner needle,while the outer needle provides a gas, e.g., so as to provide gasassistance to the electrospinning process. In some embodiments, theinner needle has any suitable inner diameter, such as 0.05 to 1 mm (and,e.g., an outer diameter of 0.2 to 1.5 mm), and the outer needle havingany suitable inner diameter (which is greater than the outer diameter ofthe inner needle), such as 0.7 to 2 mm. The gas applied to, or providedby, the outer needle has any suitable velocity, such as 50 m/s to 1,000m/s, or 200 m/s to 500 m/s. The flow rate of any fluid stock providedherein (e.g., to the inner needle) is any suitable rate (e.g., the ratemay be much higher with common axial gas assistance than would otherwisebe possible) 1×10⁻¹¹ to 1×10⁻⁹ m/s. Any suitable charge is applied tothe nozzle apparatus (e.g., to the inner needle) and/or the collector.For example, a change of +5 kV to +30 kV (e.g., about +20 kV) isoptionally applied to the collector. Further, any suitable distancebetween the nozzle apparatus and the collector is optionally utilized(e.g., 5-25 cm, about 10 cm, or the like).

In specific embodiments, the process comprises coaxial electrospinning(electrospinning two or more fluids about a common axis). As describedherein, coaxial electrospinning a first fluid stock as described herein(i.e., comprising a metal reagent component and a polymer) with a secondfluid is used to add coatings, make hollow nanofibers, make nanofiberscomprising more than one material, and the like. In various embodiments,the second fluid is either outside (i.e., at least partiallysurrounding) or inside (e.g., at least partially surrounded by) thefirst fluid stock. In some embodiments, the second fluid is a gas(gas-assisted electrospinning). In some embodiments, gas assistanceincreases the throughput of the process, reduces the diameter of thenanofibers, and/or is used to produce hollow nanofibers. In someembodiments, the method for producing nanofibers comprises coaxiallyelectrospinning the first fluid stock and a gas. In other embodiments,the second fluid is a second fluid stock having the characteristics asdescribed herein (i.e., comprising a polymer and metal reagent componentaccording to the instant disclosure).

The term “alkyl” as used herein, alone or in combination, refers to anoptionally substituted straight-chain, or optionally substitutedbranched-chain saturated or unsaturated hydrocarbon radical. Examplesinclude, but are not limited to methyl, ethyl, n-propyl, isopropyl,2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl,3-methyl-1-butyl, 2-methyl-3-butyl, 2,2-dimethyl-1-propyl,2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl,2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, n-butyl,isobutyl, sec-butyl, t-butyl, n-pentyl, isopentyl, neopentyl, tert-amyland hexyl, and longer alkyl groups, such as heptyl, octyl and the like.Whenever it appears herein, a numerical range such as “C₁-C₆ alkyl,”means that: in some embodiments, the alkyl group consists of 1 carbonatom; in some embodiments, 2 carbon atoms; in some embodiments, 3 carbonatoms; in some embodiments, 4 carbon atoms; in some embodiments, 5carbon atoms; in some embodiments, 6 carbon atoms. The presentdefinition also covers the occurrence of the term “alkyl” where nonumerical range is designated. In certain instances, “alkyl” groupsdescribed herein include linear and branched alkyl groups, saturated andunsaturated alkyl groups, and cyclic and acyclic alkyl groups.

The term “aryl” as used herein, alone or in combination, refers to anoptionally substituted aromatic hydrocarbon radical of six to abouttwenty ring carbon atoms, and includes fused and non-fused aryl rings. Afused aryl ring radical contains from two to four fused rings, where thering of attachment is an aryl ring, and the other individual rings arealicyclic, heterocyclic, aromatic, heteroaromatic or any combinationthereof. Further, the term aryl includes fused and non-fused ringscontaining from six to about twelve ring carbon atoms, as well as thosecontaining from six to about ten ring carbon atoms. A non-limitingexample of a single ring aryl group includes phenyl; a fused ring arylgroup includes naphthyl, phenanthrenyl, anthracenyl, azulenyl; and anon-fused bi-aryl group includes biphenyl.

The term “heteroaryl” as used herein, alone or in combination, refers tooptionally substituted aromatic monoradicals containing from about fiveto about twenty skeletal ring atoms, where one or more of the ring atomsis a heteroatom independently selected from among oxygen, nitrogen,sulfur, phosphorous, silicon, selenium and tin but not limited to theseatoms and with the proviso that the ring of the group does not containtwo adjacent O or S atoms. Where two or more heteroatoms are present inthe ring, in some embodiments, the two or more heteroatoms are the sameas each another; in some embodiments, some or all of the two or moreheteroatoms are be different from the others. The term heteroarylincludes optionally substituted fused and non-fused heteroaryl radicalshaving at least one heteroatom. The term heteroaryl also includes fusedand non-fused heteroaryls having from five to about twelve skeletal ringatoms, as well as those having from five to about ten skeletal ringatoms. In some embodiments, bonding to a heteroaryl group is via acarbon atom; in some embodiments, via a heteroatom. Thus, as anon-limiting example, an imidazole group is attached to a parentmolecule via any of its carbon atoms (imidazol-2-yl, imidazol-4-yl orimidazol-5-yl), or its nitrogen atoms (imidazol-1-yl or imidazol-3-yl).Further, in some embodiments, a heteroaryl group is substituted via anyor all of its carbon atoms, and/or any or all of its heteroatoms. Afused heteroaryl radical contains from two to four fused rings, wherethe ring of attachment is a heteroaromatic ring. In some embodiments,the other individual rings are alicyclic, heterocyclic, aromatic,heteroaromatic or any combination thereof. A non-limiting example of asingle ring heteroaryl group includes pyridyl; fused ring heteroarylgroups include benzimidazolyl, quinolinyl, acridinyl; and a non-fusedbi-heteroaryl group includes bipyridinyl. Further examples ofheteroaryls include, without limitation, furanyl, thienyl, oxazolyl,acridinyl, phenazinyl, benzimidazolyl, benzofuranyl, benzoxazolyl,benzothiazolyl, benzothiadiazolyl, benzothiophenyl, benzoxadiazolyl,benzotriazolyl, imidazolyl, indolyl, isoxazolyl, isoquinolinyl,indolizinyl, isothiazolyl, isoindolyloxadiazolyl, indazolyl, pyridyl,pyridazyl, pyrimidyl, pyrazinyl, pyrrolyl, pyrazinyl, pyrazolyl,purinyl, phthalazinyl, pteridinyl, quinolinyl, quinazolinyl,quinoxalinyl, triazolyl, tetrazolyl, thiazolyl, triazinyl, thiadiazolyland the like, and their oxides, such as for example pyridyl-N-oxide.

The term “heteroalkyl” as used herein refers to optionally substitutedalkyl structure, as described above, in which one or more of theskeletal chain carbon atoms (and any associated hydrogen atoms, asappropriate) are each independently replaced with a heteroatom (i.e. anatom other than carbon, such as though not limited to oxygen, nitrogen,sulfur, silicon, phosphorous, tin or combinations thereof), orheteroatomic group such as though not limited to —O—O—, —S—S—, —O—S—,—S—O—, ═N—N═, —N═N—, —N═N—NH—, —P(O)2-, —O—P(O)2-, —P(O)2-O—, —S(O)—,—S(O)2-, —SnH2- and the like.

The term “heterocyclyl” as used herein, alone or in combination, referscollectively to heteroalicyclyl groups. Herein, whenever the number ofcarbon atoms in a heterocycle is indicated (e.g., C1-C6 heterocycle), atleast one non-carbon atom (the heteroatom) must be present in the ring.Designations such as “C1-C6 heterocycle” refer only to the number ofcarbon atoms in the ring and do not refer to the total number of atomsin the ring. Designations such as “4-6 membered heterocycle” refer tothe total number of atoms that are contained in the ring (i.e., a four,five, or six membered ring, in which at least one atom is a carbon atom,at least one atom is a heteroatom and the remaining two to four atomsare either carbon atoms or heteroatoms). For heterocycles having two ormore heteroatoms, in some embodiments, those two or more heteroatoms arethe same; in some embodiments, they are different from one another. Insome embodiments, heterocycles are substituted. Non-aromaticheterocyclic groups include groups having only three atoms in the ring,while aromatic heterocyclic groups must have at least five atoms in thering. In some embodiments, bonding (i.e. attachment to a parent moleculeor further substitution) to a heterocycle is via a heteroatom; in someembodiments, via a carbon atom.

In specific embodiments, a “substituted” group is optionally substitutedwith one or more of H, halo, CN, OH, NO₂, NH₂, NH(alkyl) orN(alkyl)(alkyl), SO₂alkyl, CO₂-alkyl, alkyl, heteroalkyl, alkoxy,S-alkyl, cycloalkyl, heterocycle, aryl, or heteroaryl.

EXAMPLES Example 1—Preparing a Fluid Stock of Nickel Acetate and PVA

Two (2) grams of nickel acetate, the metal precursor, was dissolved in20 ml of 1 molar acetic acid solution. The solution was stirred for 2hours to create a solution of nickel acetate. The solution washomogenous.

In a second solution, 1 gram of 99.7% hydrolyzed polyvinyl alcohol (PVA)with an average molecular weight of 79 kDa and polydispersity index of1.5 was dissolved in 10 ml of de-ionized water. The polymer solution washeated to a temperature of 95° C. and stirred for 2 hours to create ahomogenous solution.

The nickel acetate solution was then combined with the PVA solution tocreate a fluid stock. In order to distribute the precursor substantiallyevenly in the fluid stock, the precursor solution was added gradually tothe polymer solution while being continuously vigorously stirred for 2hours. The mass ratio of precursor to polymer for the fluid feed (basedon initial nickel acetate mass) was 2:1.

Example 2—Characterization of a Fluid Stock of Nickel Acetate and PVA

The chemical interaction between the ligand of the metal precursor andthe functional group in the polymer backbone resulted in extremely highloading of metal precursors without losing the spinnability. Theinteraction was demonstrated in the FT-IR study for nanofibers withvarious ratios of PVA to Ni precursor. As demonstrated in FIG. 4, thereduction of —OH bond and increase in —CO bond were observed at highloading of Ni precursor (Ni:PVA=4:1).

Example 3—Electrospinning a Fluid Stock of Nickel Acetate and PVA

The fluid stock of Example 1 was electrospun by a gas-assistedtechnique. The overall process and apparatus is depicted in FIG. 5,Panel A. The fluid stock was loaded into a syringe pump connected to aspinneret with an inner nozzle diameter (fluid stock) of 4.13×10⁻⁴ m andan outer (air) diameter of 1.194×10¹ m. The distance between the nozzleand the collection plate was kept at about 15 cm and the fluid stock wasspun at a rate of 0.1 ml/min. A charge of +15 kV was maintained at thecollector. The air velocity at the nozzle was 100 m/s. The temperatureof the air and fluid stock at the nozzle was 300 K.

Example 4—Copper Acetate and PVA Fluid Stock and Nanofiber

Following the procedure of Example 1, a fluid stock of copper acetateand PVA were prepared with ratios of precursor:polymer of 2:1. Thesefluid stocks were electrospun by the procedure of Example 3. FIG. 5,Panel B illustrates such electrospun nanofibers, having a diameter ofapproximately 600-800 nm as spun.

Example 5—Silver Acetate and PVA Fluid Stock and Nanofiber

Following the procedure of Example 1, a fluid stock of silver acetateand PVA were prepared with ratios of precursor:polymer of 2:1. Thesefluid stocks were electrospun by the procedure of Example 3. FIG. 5,Panel C illustrates such electrospun nanofibers, having a diameter ofapproximately 900-1200 nm as spun.

Example 6—Iron Acetate and PVA Fluid Stock and Nanofiber

Following the procedure of Example 1, a fluid stock of iron acetate andPVA were prepared with ratios of precursor:polymer of 2:1. These fluidstocks were electrospun by the procedure of Example 3. FIG. 5, Panel Dillustrates such electrospun nanofibers, having a diameter ofapproximately 300-500 nm as spun.

Example 7—Zinc Acetate and PVA Fluid Stock and Nanofiber

Following the procedure of Example 1, a fluid stock of zinc acetate andPVA were prepared with ratios of precursor:polymer of 2:1. These fluidstocks were electrospun by the procedure of Example 3. FIG. 5, Panel Eillustrates such electrospun nanofibers, having a diameter ofapproximately 500-1000 nm as spun.

Example 8—Cadmium Acetate and PVA Fluid Stock and Nanofiber

Following the procedure of Example 1, a fluid stock of cadmium acetateand PVA were prepared with ratios of precursor:polymer of 2:1. Thesefluid stocks were electrospun by the procedure of Example 3. FIG. 5,Panel F illustrates such electrospun nanofibers, having a diameter ofapproximately 800-1200 nm as spun.

Example 9—Zirconium Acetate and PVA Fluid Stock and Nanofiber

Following the procedure of Example 1, a fluid stock of zirconium acetateand PVA were prepared with ratios of precursor:polymer of 2:1. Thesefluid stocks were electrospun by the procedure of Example 3. FIG. 5,Panel G illustrates such electrospun nanofibers, having a diameter ofapproximately 800-1000 nm as spun.

Example 10—Lead Acetate and PVA Fluid Stock and Nanofiber

Following the procedure of Example 1, a fluid stock of lead acetate andPVA were prepared with ratios of precursor:polymer of 2:1. These fluidstocks were electrospun by the procedure of Example 3. FIG. 5, Panel Hillustrates such electrospun nanofibers, having a diameter ofapproximately 500-1200 nm as spun.

Example 11—Lead Acetate, Selenium Powder and PVA Fluid Stock andNanofiber

A mixture of 50/50 lead acetate and Se powder was prepared according tothe procedures of Example 1. The precursors were further made into afluid stock with PVA according to the procedure of Example 1 andelectrospun according to the procedure of Example 3 to producenanofiberrs, having a diameter of approximately 700-1300 nm as spun.

Example 12—Fluid Feeds and Nanofibers

Following procedures similar to Example 1, fluid stocks were prepared bycombining silicon acetate and PVA, iron acetate and PVA, and titaniumdioxide nanoparticles and PVA. These fluid stocks were electrospun toproduce nanofibers depicted in FIG. 7, Panels A, B, and C, respectively.

Additionally, following the procedure of Example 1, fluid stocks areprepared according to Table 3 in the identified precursor-to-polymerload ratio (based on initial precursor mass combined with the polymer).These fluid stocks are also electrospun according to the procedure ofExample 3.

TABLE 3 reagent polymer load ratio iron nitrate PVA 1:1 iron chloridePVA 2:1 (+carbon powder) iron acetate PVE 1:1 chromium acetate (89/11)zirconium chloride PVA 2:1 nickel bromide PEO 1:1 chromium methoxide PVE1.5:1   tungsten ethoxide PVA 3:1 CdClOH polyvinyl 1:1 pyridine silveracetate PEO 1:1 nickel nitrate polyacrylic 2:1 acid copper ethoxide PVA1:1 nickel chloride PVE 3:1 zirconium nitrate polyvinyl 1:1 pyridinecopper nitrate PVE 3.5:1   nickel t-butoxide PVO 1:1 copper chloridepolyacrylic 1.5:1   acid aluminum nitrate PVE 2:1 zirconium acetate(70/30)

Example 13—Metal Nanostructures

To produce metal nanofibers/nanostructures, the electrospun precursornanofibers of Examples 3-12 are heated at a rate of 1-35° C. to atemperature of 600-800° C. and held there for 10 min to 20 hours underargon or a mixture of argon and hydrogen. For example, treatment ofnanofibers produced by electrospinning fluid stocks prepared bycombining (a) nickel acetate and PVA, (b) copper acetate and PVA, (c)silver acetate and PVA, (d) iron acetate and PVA, (e) lead acetate andPVA, (f) lead acetate, selenium powder and PVA, (g) cadmium acetate,selenium powder, and PVA, (h) cadmium acetate, tellurium powder, andPVA, and (i) lead acetate, tellurium powder, and PVA were utilized toproduce nickel, copper, silver, iron, cadmium, lead, and lead-seleniumalloy nanostructures. These metal nanostructures are illustrates in FIG.6, Panels A, B, C, D, E, F, G, H, and I, respectively. Further optionalprocessing of these metal nanostructures to a desired aspect ratio isachieved by sonication.

Example 14—Metal Oxide Nanostructures

To produce metal oxide nanofibers/nanostructures, the electrospunprecursor nanofibers of Examples 3-12 are heated at a rate of 1-35° C.to a temperature of 600-800° C. and held there for 10 min to 20 hoursunder air. For example, treatment of nanofibers produced byelectrospinning fluid stocks prepared by combining (a) nickel acetateand PVA, (b) copper acetate and PVA, (c) zinc acetate and PVA, (d)cadmium acetate and PVA, and (e) zirconium acetate and PVA were utilizedto produce nickel oxide, copper oxide, zinc oxide, cadmium oxide, andzirconia nanostructures. These metal oxide nanostructures areillustrates in FIG. 10, Panels A, B, C, D, and E respectively. Furtheroptional processing of these metal oxide nanostructures to a desiredaspect ratio is achieved by sonication.

Example 15—Metal Carbide Nanofiber Nanostructures

To produce metal carbide nanofibers, the electrospun precursornanofibers of Examples 3-12 are heated at a rate of 1-35° C. to atemperature of 1000-1700° C. and held there for 10 min to 20 hours. Forexample, treatment of nanofibers produced by electrospinning fluidstocks prepared by combining silicon acetate and PVA, iron acetate andPVA, and titanium dioxide nanoparticles and PVA, were utilized toproduce silicon carbide nanofibers, iron carbide nanofibers, andtitanium carbide nanofibers. These metal carbide nanofibers areillustrates in FIG. 7, Panels D, E, and F, respectively. Singlenanofibers and x-ray crystal diffraction patterns for such nanofibersare illustrated in FIG. 8, Panels A, B, and C, respectively.

Example 16—Nanocomposite Nanostructures

To produce coaxially layered composite nanofibers/nanostructures, afirst fluid feed comprising a first metal precursor and first polymer iscoaxially electrospun with a second fluid feed comprising a second metalprecursor and a second polymer (which may be the same or different fromthe first). The electrospun precursor nanofibers are then heated at arate of 1-35° C. to a temperature of 600-800° C. and held there for 10min to 20 hours under air, argon, a mixture of argon and hydrogen, or asequence thereof (e.g., first air and then a mixture of hydrogen andargon if a zirconia/metal nanocomposite is desired). For example,treatment of nanofibers produced by coaxially electrospinning fluidstocks of (a) zinc acetate/PVA and zirconium acetate/PVA, (b) silveracetate/PVA and zirconium acetate/PVA; (c) nickel acetate/PVA andzirconium acetate/PVA, (d) iron acetate/PVA and zirconium acetate/PVA,(e) nickel acetate/PVA and aluminum acetate/PVA, and (f) ironacetate/PVA and iron acetate/nickel acetate/PVA were utilized to producecoaxially layered nanostructures of zinc oxide/zirconia,silver/zirconia, nickel/zirconia, iron/zirconia, nickel/alumina, andiron oxide/iron-nickel alloy. These nanocomposite nanostructures areillustrates in FIG. 11, Panels A, B, C, D, E, and F respectively.Further optional processing of these nanocomposite nanostructures to adesired aspect ratio is achieved by sonication.

Example 17—Continuous Carbon Matrix, Discrete Metal Domain NanofiberNanostructures

To produce metal carbide nanofibers, the electrospun precursornanofibers of Examples 3-12 are heated at a rate of 1-35° C. to atemperature of 400-1200° C. and held there for 10 min to 20 hours.

What is claimed is:
 1. A nanofiber comprising a metal precursor and apolymer, the weight-to-weight ratio of the metal precursor to thepolymer being at least 1:2, at least 20% of the metal precursor beingassociated with the polymer.
 2. The nanofiber of claim 1, wherein theweight-to-weight ratio of the metal precursor to the polymer is at least1:1.
 3. The nanofiber of claim 2, wherein the weight-to-weight ratio ofthe metal precursor to the polymer is at least 2:1.
 4. The nanofiber ofclaim 1, wherein at least 50% of the metal precursor is associated withthe polymer.
 5. The nanofiber of claim 4, wherein at least 85% of themetal precursor is associated with the polymer.
 6. The nanofiber ofclaim 1, wherein at least 20% of the polymer is loaded with metalprecursor.
 7. The nanofiber of claim 6, wherein at least 40% of thepolymer is loaded with metal precursor.
 8. The nanofiber of claim 7,wherein at least 60% of the polymer is loaded with metal precursor. 9.The nanofiber of claim 8, wherein at least 80% of the polymer is loadedwith metal precursor.
 10. The nanofiber of claim 1, wherein the polymeris polyvinylalcohol (PVA), polyethylene oxide (PEO), polyvinyl ether,polyvinyl pyrrolidone (PVP), polyglycolic acid, hydroxyethylcellulose(“HEC”), ethylcellulose, cellulose ethers, polyacrylic acid,polyisocyanate.
 11. The nanofiber of claim 10, wherein the polymer ispolyvinylalcohol (PVA) or polyethylene oxide (PEO).
 12. The nanofiber ofclaim 1, wherein the metal precursor is a silicon precursor.
 13. Thenanofiber of claim 1, wherein the metal precursor comprises a metalacetate, metal alkoxide, a metal halide, a metal diketone, a metalcarboxylate, a metal nitrate, a metal amine, or a combination thereof.14. A fluid composition comprising a metal precursor, a polymer, and anaqueous medium, the weight-to-weight ratio of the metal precursor to thepolymer being at least 2:1, at least 20% of the metal precursor beingassociated with the polymer.
 15. The fluid composition of claim 14,wherein at least 50% of the metal precursor is associated with thepolymer.
 16. The fluid composition of claim 15, wherein at least 85% ofthe metal precursor is associated with the polymer.
 17. The fluidcomposition of claim 14, wherein at least 40% of the polymer is loadedwith metal precursor.
 18. The fluid composition of claim 14, wherein thepolymer is polyvinylalcohol (PVA), polyethylene oxide (PEO), polyvinylether, polyvinyl pyrrolidone (PVP), polyglycolic acid,hydroxyethylcellulose (“HEC”), ethylcellulose, cellulose ethers,polyacrylic acid, polyisocyanate.
 19. The fluid composition of claim 18,wherein the polymer is polyvinylalcohol (PVA) or polyethylene oxide(PEO).
 20. The fluid composition of claim 14, wherein the metalprecursor comprises a metal acetate, metal alkoxide, a metal halide, ametal diketone, a metal carboxylate, a metal nitrate, a metal amine, ora combination thereof.